On April 15, 2013, two homemade bombs detonated 12 seconds and 210 yards (190 m) apart at 2:49 p.m., near the finish line of the annual Boston Marathon, killing three people and injuring several hundred others, including 16 who lost limbs.  
On April 18, the Federal Bureau of Investigation (FBI) released images of two suspects,   who were later identified as Kyrgyz -American brothers Dzhokhar Tsarnaev and Tamerlan Tsarnaev. The brothers killed an MIT policeman, kidnapped a man in his car, and had a shootout with the police in nearby Watertown, during which two officers were severely injured, one of whom died a year later. Tamerlan Tsarnaev was shot several times, and his brother ran him over while escaping in the stolen car; Tamerlan died soon after.
An unprecedented manhunt for Dzhokhar Tsarnaev ensued on April 19, with thousands of law enforcement officers searching a 20-block area of Watertown;  residents of Watertown and surrounding communities were asked to stay indoors, and the transportation system and most businesses and public places closed.   Around 6:00 p.m., a Watertown resident discovered Dzhokhar hiding in a boat in his backyard. He was shot and wounded by police before being taken into custody.
During questioning, Dzhokhar alleged that he and his brother were motivated by extremist Islamist beliefs and the wars in Iraq and Afghanistan, that they were self-radicalized and unconnected to any outside terrorist groups, and that he was following his brother's lead. He said they learned to build explosive devices from an online magazine of the al-Qaeda affiliate in Yemen. He also said they had intended to travel to New York City to bomb Times Square. On April 8, 2015, he was convicted of 30 charges, including use of a weapon of mass destruction and malicious destruction of property resulting in death.  The following month, he was sentenced to death. 
The 117th annual Boston Marathon was run on Patriots' Day, April 15, 2013. At 2:49 p.m. EDT (18:49 UTC), two bombs detonated about 210 yards (190 m) apart at the finish line on Boylston Street near Copley Square.    The first exploded outside Marathon Sports at 671–673 Boylston Street at 2:49:43 p.m.  At the time of the first explosion, the race clock at the finish line showed 04:09:43,  reflecting the elapsed time since the Wave 3 start at 10:40 a.m. The second bomb exploded at 2:49:57 p.m.,   about 12 seconds later and one block farther west at 755 Boylston Street.  The explosions took place nearly three hours after the winner crossed the finish line,  but with more than 5,700 runners yet to finish. 
Casualties and initial response
Rescue workers and medical personnel, on hand as usual for the marathon, gave aid as additional police, fire, and medical units were dispatched,  including from surrounding cities as well as private ambulances from all over the state. The explosions killed 3 civilians and injured an estimated 264 others, who were treated at 27 local hospitals. At least 14 people required amputations, with some suffering traumatic amputations as a direct result of the blasts.
Police, following emergency plans, diverted arriving runners to Boston Common and Kenmore Square. The nearby Lenox Hotel and other buildings were evacuated.  Police closed a 15-block area around the blast site; this was reduced to a 12-block crime scene on April 16.  Boston police commissioner Edward F. Davis recommended that people stay off the streets.
Dropped bags and packages, abandoned as their owners fled from the blasts, increased uncertainty as to the possible presence of more bombs.   There were false reports of more bombs.        An unrelated electrical fire at the John F. Kennedy Presidential Library in nearby Dorchester was initially feared to be a bomb.
The Massachusetts Emergency Management Agency suggested people trying to contact those in the vicinity use text messaging instead of voice calls because of crowded cellphone lines.  Cellphone service in Boston was congested but remained in operation, despite some local media reports stating that cell service was shut down to prevent cell phones from being used as detonators. 
The American Red Cross helped concerned friends and family receive information about runners and casualties.   The Boston Police Department also set up a helpline for people concerned about relatives or acquaintances to contact and a line for people to provide information.  Google Person Finder activated their disaster service under Boston Marathon Explosions to log known information about missing persons as a publicly viewable file. 
Due to the closure of several hotels near the blast zone, a number of visitors were left with nowhere to stay; many Boston-area residents opened their homes to them. 
The Federal Bureau of Investigation led the investigation, assisted by the Bureau of Alcohol, Tobacco, Firearms and Explosives, the Central Intelligence Agency, the National Counterterrorism Center, and the Drug Enforcement Administration,  and they named two official suspects. It was initially believed by some that North Korea was behind the attack after escalating tensions and threats with the U.S.  
United States government officials stated that there had been no intelligence reports which indicated that such a bombing would take place. Representative Peter King, a member of the House Intelligence Committee, said: "I received two top secret briefings last week on the current threat levels in the United States, and there was no evidence of this at all." 
The father of the suspects claimed that the FBI had been watching his family, and that they questioned his sons in Cambridge, Massachusetts five times in relation to possible explosions on the streets of Boston. 
Evidence found near the blast sites included bits of metal, nails, ball bearings, black nylon pieces from a backpack,  remains of an electronic circuit board, and wiring.  A pressure cooker lid was found on a nearby rooftop.  Both of the improvised explosive devices were pressure cooker bombs manufactured by the bombers.    Authorities confirmed that the brothers used bomb-making instructions found in Al Qaeda in the Arabian Peninsula's Inspire magazine.   After the suspects were identified, The Boston Globe reported that Tamerlan purchased fireworks from a fireworks store in New Hampshire. 
On April 19, the FBI, West New York Police Department, and Hudson County Sheriff's Department seized computer equipment from the apartment of the Tamerlans' sister, located in West New York, New Jersey.  On April 24, the FBI and the Department of Homeland Security reported that their investigators had reconstructed the bombs, and believed that they had been triggered by remote controls used for toy cars. 
April 18–19 shootings and manhunt
Release of suspect photos
Jeff Bauman was immediately adjacent to one of the bombs and lost both legs; he wrote while in the hospital: "Bag, saw the guy, looked right at me". He later gave a detailed description which enabled the photo to be identified and circulated quickly. 
At 5:20 p.m. on April 18, the FBI released images of two suspects carrying backpacks, asking the public's help in identifying them.  The FBI said that they were doing this in part to limit harm to persons wrongly identified by news reports and on social-media. As seen on video, the suspects stayed to observe the chaos after the explosions, then walked away casually. The public sent authorities a deluge of photographs and videos, which were scrutinized by both authorities and online public social networks. 
MIT shooting and carjacking
A few hours after the photos were released, the Tsarnaev brothers shot Sean A. Collier of the Massachusetts Institute of Technology Police Department six times in an attempt to steal his gun, which they could not get out because of the holster's retention system.  Collier, aged 27, was seated in his police car near the Stata Center (Building 32) on the Massachusetts Institute of Technology campus. He died soon after. 
The brothers then carjacked a Mercedes-Benz M-Class SUV in the Allston-Brighton neighborhood of Boston. Tamerlan took the owner hostage and told him that he was responsible for the Boston bombing and for killing a police officer. Dzhokhar followed them in the green Honda, later joining them in the Mercedes-Benz. Interrogation later revealed that the brothers "decided spontaneously" that they wanted to go to New York and bomb Times Square. 
The Tsarnaev brothers forced the hostage to use his ATM cards to obtain $800 in cash.  They transferred objects to the Mercedes-Benz and one brother followed it in their Honda Civic,  for which an all-points bulletin was issued. The car's owner and hostage was Chinese national Dun Meng, referred to as "Danny" in early reports.  He escaped while the Tsarnaev brothers stopped at a gas station and ran across the street to another gas station, asking the clerk to call 911.   His cell phone remained in the vehicle, allowing the police to focus their search on Watertown. 
Shortly after midnight on April 19, Watertown police officer Joseph Reynolds identified the brothers in the Honda Civic and the stolen SUV. A gunfight followed between the brothers and police arriving at the scene on the 100 block of Laurel St.  An estimated 200 to 300 rounds of ammunition were fired and at least one further bomb and several "crude grenades " were thrown. 
According to Watertown Police Chief Edward Deveau, the brothers had an " arsenal of guns."  Tamerlan ran out of ammunition and threw his empty pistol at an officer, who tackled him with help from another officer.   Tamerlan's younger brother Dzhokhar then drove the stolen SUV toward Tamerlan and police who unsuccessfully tried to drag Tamerlan out of his path;   the car ran over Tamerlan and dragged him a short distance down the street.     Dzhokhar abandoned the car half a mile away and fled on foot.   Tamerlan Tsarnaev died at 1:35 a.m. at a Boston hospital.
Massachusetts Bay Transportation Authority Police Officer Richard H. Donohue Jr.  was also critically wounded  but survived.  Boston Police Department officer Dennis Simmonds was injured by a hand grenade and died April 10, 2014. Fifteen other officers were also injured.  A later report by Harvard Kennedy School's Program on Crisis Leadership concluded that lack of coordination among police agencies had put the public at excessive risk during the shootout.
Identification and search for suspects
The men were identified via registration records on their Honda at the scene,  as two brothers whose family had immigrated to the United States seeking political asylum around 2002: 26-year-old Tamerlan Tsarnaev and 19-year-old Dzhokhar "Jahar" Tsarnaev.   The FBI released additional photos of the two during the Watertown incident.  Early on April 19, Watertown residents received reverse 911 calls asking them to stay indoors.  On the morning of April 19, Governor Patrick asked residents of Watertown and adjacent cities and towns  to " shelter in place ".  Somerville residents also received a reverse-911 call with orders to shelter in place. 
A 20-block area of Watertown was cordoned off and residents were told not to leave their homes or answer the door, as officers scoured the area in tactical gear. Helicopters circled the area and SWAT teams in armored vehicles moved through in formation, with officers going door to door. On the scene were the FBI, the Bureau of Alcohol, Tobacco, Firearms and Explosives, the Department of Homeland Security, the National Guard, the Boston and Watertown Police departments, and the Massachusetts State Police. The show of force was the first major field test of the interagency task forces created in the wake of the September 11 attacks. 
The entire public transit network and most Boston taxi services were suspended, as was Amtrak service to and from Boston. Logan International Airport remained open under heightened security. Universities, schools, many businesses, and other facilities were closed as thousands of law enforcement personnel participated in the door-to-door manhunt in Watertown, as well as following up other leads, including at the house that the brothers shared in Cambridge. Seven improvised explosive devices were recovered by bomb squads. 
The brothers' father spoke from his home in Makhachkala, Dagestan, encouraging his son to: "Give up. Give up. You have a bright future ahead of you. Come home to Russia." He continued, "If they killed him, then all hell would break loose."  On television, Dzhokhar's uncle from Montgomery Village, Maryland, pleaded with him to turn himself in. 
David Henneberry, a Watertown resident outside the search area, noticed that the tarp was loose on his parked boat on the evening of April 19, two hours after the shelter-in-place order had been lifted.   He then saw a body lying inside the boat in a pool of blood. Authorities surrounded the boat and a police helicopter verified movement through a thermal imaging device.   The person inside the boat started poking at the tarp, and police shot at the boat.
According to Boston Police Commissioner Ed Davis and Watertown Police Chief Deveau, Dzhokhar Tsarnaev was shooting at police from inside the boat, "exchanging fire for an hour". A subsequent report indicated that the firing lasted for a shorter period of time. The suspect was found to have no weapon when he was captured. He was arrested at 8:42 p.m.   and taken to Beth Israel Deaconess Medical Center, where he was listed in critical condition with gunshot wounds to the head, neck, legs, and hand. 
Initial reports that the neck wound represented a suicide attempt were contradicted by his being unarmed.  The situation was chaotic according to a police source quoted by the Washington Post, and the firing of weapons occurred during "the fog of war". A subsequent review by the Commonwealth of Massachusetts provided this more specific summary: "One officer fired his weapon without appropriate authority in response to perceived movement in the boat, and surrounding officers followed suit in a round of 'contagious fire', assuming they were being fired on by the suspect. Weapons continued to be fired for several seconds until on scene supervisors ordered a ceasefire and regained control of the scene. The unauthorized shots created another dangerous crossfire situation". 
United States Senators Kelly Ayotte, Saxby Chambliss, Lindsey Graham, and John McCain, and Representative Peter T. King suggested that Dzhokhar Tsarnaev, a U.S. citizen, should be tried as an unlawful enemy combatant rather than as a criminal, potentially preventing him from obtaining legal counsel.   Others said that doing so would be illegal, including prominent American legal scholar and lawyer Alan Dershowitz, and would jeopardize the prosecution.   The government decided to try Dzhokhar in the federal criminal court system and not as an enemy combatant. 
Dzhokhar was questioned for 16 hours by investigators but stopped communicating with them on the night of April 22 after Judge Marianne Bowler read him a Miranda warning.   Dzhokhar had not previously been given a Miranda warning, as federal law enforcement officials invoked the warning's public safety exception.  This raised doubts whether his statements during this investigation would be admissible as evidence and led to a debate surrounding Miranda rights.  
Charges and detention
On April 22, 2013, formal criminal charges were brought against Tsarnaev in the United States District Court for the District of Massachusetts during a bedside hearing while he was hospitalized. He was charged with use of a weapon of mass destruction and with malicious destruction of property resulting in death.  Some of the charges carry potential sentences of life imprisonment or the death penalty. Tsarnaev was judged to be awake, mentally competent, and lucid, and he responded to most questions by nodding. The judge asked him whether he was able to afford an attorney and he said no; he was represented by the Federal Public Defender's office.  On April 26, Dzhohkar Tsarnaev was moved from Beth Israel Deaconess Medical Center to the Federal Medical Center at Fort Devens, about 40 miles (64 km) from Boston. FMC Devens is a federal prison medical facility at a former Army base  where he was held in solitary confinement at a segregated housing unit  with 23-hour-per-day lockdown.  
On July 10, 2013, Tsarnaev pleaded not guilty to 30 charges in his first public court appearance, including a murder charge for MIT police officer Sean Collier.  He was back in court for a status hearing on September 23,  and his lawyers requested more time to prepare their defense. On October 2, Tsarnaev's attorneys asked the court to lift the special administrative measures (SAMs) imposed by Attorney General Holder in August, saying that the measures had left Tsarnaev unduly isolated from communication with his family and lawyers, and that no evidence suggested that he posed a future threat.
Trial and sentencing
Jury selection began on January 5, 2015 and was completed on March 3, with a jury consisting of eight men and 10 women (including six alternates). The trial began on March 4 with Assistant U.S. Attorney William Weinreb describing the bombing and painting Dzhokhar as "a soldier in a holy war against Americans" whose motive was "reaching paradise". He called the brothers equal participants. 
Defense attorney Judy Clarke admitted that Dzhokhar Tsarnaev had placed the second bomb and was present at the murder of Sean Collier, the carjacking of Dun Meng, and the Watertown shootout, but she emphasized the influence that his older brother had on him, portraying him as a follower.  Between March 4 and 30, prosecutors called more than 90 witnesses, including bombing survivors who described losing limbs in the attack, and the government rested its case on March 30.  The defense rested as well on March 31, after calling four witnesses.
Tsarnaev was found guilty on all 30 counts on April 8.  The sentencing phase of the trial began April 21,  and a further verdict was reached on May 15 recommending that he be put to death.  Tsarnaev was sentenced to death on June 24, after apologizing to the victims. 
Motives and backgrounds of Tsarnaev brothers
According to FBI interrogators, Dzhokhar and his brother were motivated by Islamic beliefs but "were not connected to any known terrorist groups", instead learning to build explosive weapons from an online magazine published by al-Qaeda affiliates in Yemen. They further alleged that "[Dzhokhar and] his brother considered suicide attacks and striking [the Boston Pops Fireworks Spectacular] on the Fourth of July; but ultimately decided to use pressure cooker bombs (capable of remote detonation) and other IEDs." Fox News reported that the brothers "chose the prestigious race as a 'target of opportunity' ... [after] the building of the bombs came together more quickly than expected". 
Dzhokhar said that he and his brother wanted to defend Islam from the U.S., accusing the U.S. of conducting the Iraq War and War in Afghanistan against Muslims.   A CBS report revealed that Dzhokhar had scrawled a note with a marker on the interior wall of the boat where he was hiding; the note stated that the bombings were "retribution for U.S. military action in Afghanistan and Iraq", and called the Boston victims " collateral damage ", "in the same way innocent victims have been collateral damage in U.S. wars around the world."   Photographs of the note were later used in the trial. 
Some political science and public policy writers suggest that Islam may have played a secondary role in the attacks. These writers theorize that the primary motives might have been sympathy towards the political aspirations in the Caucasus region and Tamerlan's inability to become fully integrated into American society. According to the Los Angeles Times, a law enforcement official said that Dzhokhar "did not seem as bothered about America's role in the Muslim world" as his brother Tamerlan had been.  Dzhokhar identified Tamerlan as the "driving force" behind the bombing, and said that his brother had only recently recruited him to help.  
Tamerlan Tsarnaev was born in 1986 in the Kalmyk Autonomous Soviet Socialist Republic, North Caucasus.  Dzhokhar was born in 1993 in Kyrgyzstan, although some reports say that his family claims that he was born in Dagestan.  The family spent time in Tokmok, Kyrgyzstan, and in Makhachkala, Dagestan.  They are half Chechen through their father Anzor, and half Avar through their mother Zubeidat. They never lived in Chechnya, yet the brothers identified themselves as Chechen.   
The Tsarnaev family immigrated to the United States in 2002   where they applied for political asylum, settling in Cambridge, Massachusetts.  Tamerlan Tsarnaev attended Bunker Hill Community College but dropped out to become a boxer. His goal was to gain a place on the U.S. Olympic boxing team, saying that, "unless his native Chechnya becomes independent", he would "rather compete for the United States than for Russia".   He married U.S. citizen Katherine Russell on July 15, 2010 in the Masjid Al Quran Mosque  in the Dorchester section of Boston; she was pregnant with their daughter.  While initially quoted in a student magazine as saying, "I don't have a single American friend. I don't understand them," a later FBI interview report documents Tamerlan stating it was a misquote, and that most of his friends were American.   He had a history of violence, including an arrest in July 2009 for assaulting his girlfriend. 
The brothers were Muslim; Tamerlan's aunt stated that he had recently become a devout Muslim.   Tamerlan became more devout and religious after 2009,   and a YouTube channel in his name linked to Salafist  and Islamist   videos. The FBI was informed by the Russian Federal Security Service (FSB) in 2011 that he was a "follower of radical Islam." In response, the FBI interviewed Tamerlan and his family and searched databases, but they did not find any evidence of "terrorism activity, domestic or foreign."      During the 2012 trip to Dagestan, Tamerlan was reportedly a frequent visitor at a mosque on Kotrova Street in Makhachkala,    believed by the FSB to be linked with radical Islam.  Some believe that "they were motivated by their faith, apparently an anti-American, radical version of Islam" acquired in the U.S.,  while others believe that the turn happened in Dagestan.
At the time of the bombing, Dzhokhar Tsarnaev was a student at the University of Massachusetts Dartmouth with a major in marine biology.  He became a naturalized U.S. citizen on September 11, 2012.  Tamerlan's boxing coach reported to NBC that the young brother was greatly affected by Tamerlan and admired him. 
Tamerlan was previously connected to the triple homicide in Waltham, Massachusetts on the evening of September 11, 2011, but he was not a suspect at the time.   Brendan Mess, Erik Weissman, and Raphael Teken were murdered in Mess's apartment. All had their throats slit from ear to ear with such great force that they were nearly decapitated. The local district attorney said that it appeared that the killer and the victims knew each other, and that the murders were not random. Tamerlan Tsarnaev had previously described murder victim Brendan Mess as his "best friend." After the bombing and subsequent revelations of Tsarnaev's personal life, the Waltham murders case was reexamined in April 2013 with Tsarnaev as a new suspect.  Both ABC and The New York Times have reported that there is strong evidence which implicates Tsarnaev in this triple homicide. 
Some analysts claim that the Tsarnaev's mother Zubeidat Tsarnaeva is a radical extremist and supporter of jihad who influenced her sons' behavior.   This prompted the Russian government to warn the U.S. government on two occasions about the family's behavior. Both Tamerlan and his mother were placed on a terrorism watch list about 18 months before the bombing took place. 
Other arrests, detentions, and prosecutions
Persons detained and released
On April 15, several people who were near the scene of the blast were taken into custody and questioned about the bombing, including a Saudi man whom police stopped as he was walking away from the explosion; they detained him when some of his responses made them uncomfortable.   Law enforcement searched his residence in a Boston suburb, and the man was found to have no connection to the attack. An unnamed U.S. official said, "he was just at the wrong place at the wrong time."   
On the night of April 18, two men riding in a taxi in the vicinity of the shootout were arrested and released shortly thereafter when police determined that they were not involved in the Marathon attacks.  Another man was arrested several blocks from the site of the shootout and was forced to strip naked by police who feared that he might have concealed explosives. He was released that evening after a brief investigation determined that he was an innocent bystander.  
On May 22, the FBI interrogated Ibragim Todashev in Orlando, Florida, who was a Chechen from Boston. During the interrogation, he was shot and killed by an FBI agent who claimed that Todashev attacked him.  The New York Times quoted an unnamed law enforcement official as saying that Todashev had confessed to a triple homicide and had implicated Tsarnaev, as well. Todashev's father claims that his son is innocent and that federal investigators are biased against Chechens and made up their case against him. 
Dias Kadyrbayev, Azamat Tazhayakov, and Robel Phillipos
Robel Phillipos (19) was a U.S. citizen of Ethiopian descent living in Cambridge who was arrested and faced with charges of knowingly making false statements to police.  He graduated from high school in 2011 with Dzhokhar Tsarnaev.  Dias Kadyrbayev (19) and Azamat Tazhayakov (20) were natives of Kazakhstan living in the U.S.    They were Dzhokhar Tsarnaev's roommates in an off-campus housing complex in New Bedford, Massachusetts at which Tsarnaev had sometimes stayed. 
Phillipos, Kadyrbayev, Tazhayakov, and Tsarnaev entered the University of Massachusetts Dartmouth in the fall of 2011 and knew each other well. After seeing photos of Tsarnaev on television, the three men traveled to his dorm room where they retrieved a backpack and laptop belonging to Tsarnaev. The backpack was discarded, but police recovered it and its contents in a nearby New Bedford landfill on April 26. During interviews, the men initially denied visiting the dorm room but later admitted their actions. 
Arrests and legal proceedings
Kadyrbayev and Tazhayakov were arrested by police at the off-campus housing complex during the night of April 18–19. An unidentified girlfriend of one of the men was also arrested,    but all three were soon released. 
Kadyrbayev and Tazhayakov were re-arrested in New Bedford on April 20 and held on immigration-related violations. They appeared before a federal immigration judge on May 1 and were charged with overstaying their student visas.   That same day, Kadyrbayev and Tazhayakov were charged criminally with:
willfully conspir(ing) with each other to commit an offense against the United States… by knowingly destroying, concealing, and covering up objects belonging to Dzhokhar Tsarnaev, namely, a backpack containing fireworks and a laptop computer, with the intent to impede, obstruct, and influence the criminal investigation of the Marathon bombing.  
Kadyrbayev and Tazhayakov were indicted by a federal grand jury on August 8, 2013 on charges of conspiracy to obstruct justice for helping Dzhokhar Tsarnaev dispose of a laptop computer, fireworks, and a backpack after the bombing. Each faced up to 25 years in prison and deportation if convicted. Tazhayakov was convicted of obstruction of justice and conspiracy on July 21, 2014. 
Kadyrbayev pleaded guilty to obstruction charges on August 22, 2014,  but sentencing was delayed pending the U.S. Supreme Court's ruling in Yates v. United States.  Kadyrbayev was sentenced to six years in prison in June 2015. 
Tazhayakov pleaded not guilty and went to trial, arguing that "Kadyrbayev was the mastermind behind destroying the evidence and that Tazhayakov only 'attempted obstruction.'" Jurors returned a guilty verdict against him, however, and he was sentenced to 42 months in prison in June 2015, which equated to three and a half years. Judge Douglas Woodlock gave a lighter sentence to Tazahayakov than to Kadyrbayev, who was viewed as more culpable.  Tazhayakov was released in May 2016 and subsequently deported. 
Phillipos was arrested and faced charges of knowingly making false statements to police.  He was released on $100,000 bail and placed under house confinement with an ankle monitor.  He was convicted on October 28, 2014, on two charges of lying about being in Tsarnaev's dorm room. He later acknowledged that he had been in the room while two friends removed a backpack containing potential evidence relating to the bombing.
Phillipos faced a maximum sentence of eight years' imprisonment on each count. In June 2015, U.S. District Judge Douglas P. Woodlock sentenced him to three years in prison.  Phillipos filed an appeal, but his sentence was upheld in court on February 28, 2017. 
A federal indictment was unsealed against Khairullozhon Matanov on May 30, 2014, charging him with "one count of destroying, altering, and falsifying records, documents, and tangible objects in a federal investigation, specifically information on his computer, and three counts of making materially false, fictitious, and fraudulent statements in a federal terrorism investigation." Matanov bought dinner for the two Tsarnaev brothers 40 minutes after the bombing. After the Tsarnaev brothers' photos were released to the public, Matanov viewed the photos on the CNN and FBI websites before attempting to reach Dzhokhar, and then tried to give away his cell phone and delete hundreds of documents from his computer. Prosecutors said that Matanov attempted to mislead investigators about the nature of his relationship with the brothers and to conceal that he shared their philosophy of violence.  
Matanov was originally from Kyrgyzstan. He came to the U.S. in 2010 on a student visa, and later claimed asylum. He attended Quincy College for two years before dropping out to become a taxicab driver. He was living in Quincy, Massachusetts at the time of his arrest, and was a friend of Tamerlan Tsarnaev. 
Three civilians were killed in the bombing: Krystle Marie Campbell (29), a restaurant manager from Medford, Massachusetts;  Lü Lingzi (Chinese: 吕令子)   (23), a Chinese national and Boston University graduate student from Shenyang, Liaoning;  and 8-year old Martin William Richard from the Dorchester neighborhood of Boston, who was killed by the second bomb. 
Sean A. Collier (27) was ambushed in his police car on April 18, at about 10:48 p.m. He was an MIT police officer, and had been with the Somerville Auxiliary Police Department from 2006 to 2009.  He died from multiple gunshot wounds from the bombers.
Boston Police Department officer Dennis Simmonds died on April 10, 2014—nearly a year later—as a result of injuries which he sustained from a hand grenade during the Watertown shootout.
According to the Boston Public Health Commission, 264 civilians were treated at 27 local hospitals. Eleven days later, 29 remained hospitalized, one in critical condition.  Many victims had lower leg injuries and shrapnel wounds,  which indicated that the devices were low to the ground.  At least 16 civilians lost limbs, at the scene or by amputation in a hospital, and three lost more than one limb.  
Doctors described removing "ball-bearing type" metallic beads a little larger than BBs and small carpenter-type nails about 0.5 to 1 inch (1 to 3 cm) long.  Similar objects were found at the scene. The New York Times cited doctors as saying that the bombs mainly injured legs, ankles, and feet because they were low to the ground, instead of fatally injuring abdomens, chests, shoulders, and heads. Some victims had perforated eardrums. 
MBTA police officer Richard H. Donohue Jr. (33) was critically wounded during a firefight with the bombers just after midnight on April 19.  He lost almost all of his blood, and his heart stopped for 45 minutes, during which time he was kept alive by cardiopulmonary resuscitation.  The Boston Globe reported that Donohue may have been accidentally shot by a fellow officer. 
Marc Fucarile lost his right leg and received severe burns and shrapnel wounds. He was the last victim released from hospital care on July 24, 2013. 
Aid to victims
The One Fund Boston was established by Massachusetts Governor Deval Patrick and Boston mayor Thomas Menino to make monetary distributions to bombing victims.  The Boston Strong concert at the TD Garden in Boston on May 30, 2013 benefitted the One Fund, which ultimately received more than $69.8 million in donations.  A week after the bombing, crowd funding websites received more than 23,000 pledges promising more than $2 million for the victims, their families, and others affected by the bombing.  The Israel Trauma Coalition for Response and Preparedness sent six psychologists and specialists from Israel to help Boston emergency responders, government administrators, and community people develop post-terrorist attack recovery strategies. 
Numerous sporting events, concerts, and other public entertainment were postponed or cancelled in the days following the bombing.      The MBTA public transit system was under heavy National Guard and police presence and it was shut down a second time April 19 during the manhunt. 
In the days after the bombing, makeshift memorials began to spring up along the cordoned-off area surrounding Boylston Street. The largest was located on Arlington Street, the easternmost edge of the barricades, starting with flowers, tokens, and T-shirts.      In June, the Makeshift Memorial located in Copley Square was taken down and the memorial objects located there were moved to the archives in West Roxbury for cleaning, fumigation, and archiving. 
Boston University established a scholarship in honor of Lü Lingzi, a student who died in the bombing. University of Massachusetts Boston did the same in honor of alumna and bombing victim Krystle Campell.  MIT also established a scholarship and erected a sculpture (unveiled on April 29, 2015), both in memory of MIT Police officer Sean Collier.
President Barack Obama addressed the nation after the attack.  He said that the perpetrators were still unknown, but that the government would "get to the bottom of this" and that those responsible "will feel the full weight of justice".  He ordered flags to half-mast until April 20 on all federal buildings as "a mark of respect for the victims of the senseless acts of violence perpetrated on April 15, 2013 in Boston, Massachusetts." 
Moments of silence were held at various events across the country, including at the openings of the New York Stock Exchange, NASDAQ, and NYMEX on the day after the bombing. Numerous special events were held, including marathons and other runs.   
The bombing was denounced and condolences were offered by many international leaders as well as leading figures from international sport. Security measures were increased worldwide in the wake of the attack.    
In China, users posted condolence messages on Weibo in response to the death of Lü Lingzi.  Chris Buckley of The New York Times said "Ms. Lu's death gave a melancholy face to the attraction that America and its colleges exert over many young Chinese." Laurie Burkitt of The Wall Street Journal said "Ms. Lu's death resonates with many in China" due to the one-child policy. 
Organizers of the London Marathon, which was held six days after the Boston bombing, reviewed security arrangements for their event. Hundreds of extra police officers were drafted in to provide a greater presence on the streets, and a record 700,000 spectators lined the streets. Runners in London observed a 30-second silence in respect for the victims of Boston shortly before the race began, and many runners wore black ribbons on their vests. Organisers also pledged to donate US$3 to a fund for Boston Marathon victims for every person who finished the race.   
Organizers of the 2013 Vancouver Sun Run, which was held on April 21, 2013, donated $10 from every late entry for the race to help victims of the bombing at the Boston Marathon. Jamie Pitblado, vice-president of promotions for The Vancouver Sun and The Province, said the money would go to One Fund Boston, an official charity that collected donations for the victims and their families. Sun Run organizers raised anywhere from $25,000 to $40,000. There were over 48,000 participants, many dressed in blue and yellow (Boston colors) with others wearing Boston Red Sox caps. 
Petr Gandalovic, ambassador of the Czech Republic, released a statement after noticing much confusion on Facebook and Twitter between his nation and the Chechen Republic. "The Czech Republic and Chechnya are two very different entities – the Czech Republic is a Central European country; Chechnya is a part of the Russian Federation." 
Security was also stepped up in Singapore in response to online threats made on attacking several locations in the city-state and the Singapore Marathon in December. Two suspects were investigated and one was eventually arrested for making false bomb threats. 
The Russian government said special attention would be paid to security at upcoming international sports events in Russia, including the 2014 Winter Olympics.  According to the Russian embassy in the U.S., President Vladimir Putin condemned the bombing as a "barbaric crime" and "stressed that the Russian Federation will be ready, if necessary, to assist in the U.S. authorities' investigation."  He urged closer cooperation of security services with Western partners  but other Russian authorities and mass media blamed the U.S. authorities for negligence as they warned the US of the Tsarnaevs.  Moreover Russian authorities and mass media since the spring of 2014 blame USA for politically motivated false information about lack of response from Russian authorities after subsequent U.S. requests. As proof a letter from the Russian Federal Security Service (FSB) was shown to the members of an official U.S. Congressional delegation to Moscow during their visit. This letter with information about Tsarnaev (including his biography details, connections and phone number) had been sent from FSB to FBI and CIA during March 2011. 
Republican U.S. Senators Saxby Chambliss and Richard Burr reported that Russian authorities had separately asked both the FBI (at least twice: during March and November 2011) and the CIA (September 2011) to look carefully into Tamerlan Tsarnaev and provide more information about him back to Russia.  Russian Federal Security Service (FSB) secretly recorded phone conversations between Tamerlan Tsarnaev and his mother (they vaguely and indirectly discussed jihad) and sent these to the FBI as evidence of possible extremist links within the family.  However, while Russia offered US intelligence services warnings that Tsarnaev planned to link up with extremist groups abroad, an FBI investigation yielded no evidence to support those claims at the time. In addition, subsequent U.S. requests for additional information about Tsarnaev went unanswered by the Russians. 
On April 19, 2013, the press-secretary of the head of the Chechen Republic, Ramzan Kadyrov, issued a statement that, inter alia, read: "The Boston bombing suspects have nothing to do with Chechnya".   On the same day, Kadyrov was reported by The Guardian to have written on Instagram: 
Any attempt to make a link between Chechnya and the Tsarnaevs, if they are guilty, is in vain. They grew up in the U.S., their views and beliefs were formed there. The roots of evil must be searched for in America. The whole world must battle with terrorism. We know this better than anyone. We wish recover [ sic ] to all the victims and share Americans' feeling of sorrow.
Akhmed Zakayev, head of the secular wing of the Chechen separatist movement, now in exile in London, condemned the bombing as "terrorist" and expressed condolences to the families of the victims. Zakayev denied that the bombers were in any way representative of the Chechen people, saying that "the Chechen people never had and can not have any hostile feelings toward the United States and its citizens." 
The Mujahideen of the Caucasus Emirate Province of Dagestan, the Caucasian Islamist organization in both Chechnya and Dagestan, denied any link to the bombing or the Tsarnaev brothers and stated that it was at war with Russia, not the United States. It also said that it had sworn off violence against civilians since 2012.   
In the Turkistan Islamic Party's Turkestan Al-Islamiyya magazine, Issue 13, the Rohingya cleric Abu Dhar 'Azzam (Abu Dhar Al-Burmi) congratulated the Tsarnaev brothers on their terrorist attack in the Boston Marathon bombing, saying, "In the very house of unbelief, two Chechen brothers destroyed the infidels' fortresses on April 16, 2013. During the [ensuing] search [by the authorities for the perpetrators], the elder brother died as a martyr in the field of glory and honor, Allah willing. The younger brother, Dzokhar, remained, and told his dear nation: 'We did this operation as revenge for what America does in Palestine, Iraq, and Afghanistan.' He didn't mention his homeland Chechnya, since this jihad is a jihad of [an entire] nation, not [a campaign] for the liberation of a single land.... The Muslims' lands are one and their honor is one." 
Criticism of "shelter-in-place" directive and house-to-house searches
During the manhunt for the perpetrators of the bombing, Governor Deval Patrick said "we are asking people to shelter in place." The request was highly effective; most people stayed home, causing Boston, Watertown, and Cambridge to come to a virtual standstill. According to Time magazine, "media described residents complying with a 'lockdown order,' but in reality the governor's security measure was a request." Scott Silliman, emeritus director of the Center on Law, Ethics and National Security at Duke Law School, said that the shelter-in-place request was voluntary. 
The shelter-in-place directive was criticized by some commentators. Michael Cohen of The Observer said that Americans have little experience with daily terrorism compared to some countries and "are more primed to … assume the absolute worst."  Cohen wrote that it was not the first time dangerous murderers have been on the loose in a large American city (citing Christopher Dorner in 2013 and the Beltway sniper attacks in 2002), but noted that "lockdown" measures were not used in those cases.  Former congressman and presidential candidate Ron Paul, criticized what he described as a "military-style takeover of parts of Boston" during the investigation and wrote that "this unprecedented move should frighten us as much or more than the attack itself." 
Haaretz ' s Chemi Salev wrote that "in terms of cost-benefit analysis, from the evil terrorist's point of view, the Boylston Street bombings and their aftermath can only be viewed as a resounding triumph" since the "relatively amateurish" terrorists managed to intimidate a vast number of people and got a maximum amount of publicity.  Responding to Salev in The New York Times, Ross Douthat commented that the massive manhunt operation might deter other amateur terrorists, but not hard-core terrorists such as Mohammed Atta.  Douthat argued that out-of-the-ordinary measures can only be used when terrorism itself is out-of-the-ordinary: if attacks started to occur more often, people would not be as willing to comply with shelter-in-place commands, yet once a terrorist has been hunted with such an operation, it is hard to justify why such measures should not be taken the next time. 
On the afternoon of the bombing, the New York Post reported that a suspect, a Saudi Arabian male, was under guard and being questioned at a Boston hospital.  That evening, Boston Police Commissioner Ed Davis said that there had not been an arrest.  The Post did not retract its story about the suspect, leading to widespread reports by CBS News, CNN, and other media that a Middle Eastern suspect was in custody.  The day after the bombing, a majority of outlets were reporting that the Saudi was a witness, not a suspect. 
The New York Post on its April 18 front page showed two men, and said they were being sought by the authorities. The two were not the ones being sought as suspects. They were a 17-year-old boy and his track coach. The boy, from Revere, Massachusetts, turned himself over to the police immediately and was cleared after a 20-minute interview in which they advised him to deactivate his Facebook account.   New York Post editor Col Allan stated, "We stand by our story. The image was emailed to law enforcement agencies yesterday afternoon seeking information about these men, as our story reported. We did not identify them as suspects." The two were implied to be possible suspects via crowdsourcing on the websites Reddit  and 4chan. 
Several other people were mistakenly identified as suspects.  Two of those wrongly identified as suspects on Reddit were a 17-year-old track star and Sunil Tripathi, a Brown University student missing since March.   Tripathi was found dead on April 23 in the Providence River. 
On April 17, the FBI released the following statement:
Contrary to widespread reporting, no arrest has been made in connection with the Boston Marathon attack. Over the past day and a half, there have been a number of press reports based on information from unofficial sources that has been inaccurate. Since these stories often have unintended consequences, we ask the media, particularly at this early stage of the investigation, to exercise caution and attempt to verify information through appropriate official channels before reporting.  
The decision to release the photos of the Tsarnaev brothers was made in part to limit damage done to those misidentified on the Internet and by the media, and to address concerns over maintaining control of the manhunt.
A film about the Boston Marathon bombing, Patriots Day, was released in 2016.
- 2010 Times Square car bombing attempt, attempted bombing in New York City using a pressure cooker bomb and other explosive devices
- 2011 Waltham triple murder, a triple homicide to which Tamerlan Tsarnaev has been connected
- 2013 Bat Yam bus bombing, bombing of a public bus in Israel using a pressure cooker bomb
- Centennial Olympic Park bombing, a 1996 terrorist attack also targeting a public event
- List of Islamist terrorist attacks
- Patriots Day (film), dramatization of the events