On the night of Friday March 9, 2018, Casillas shot while trying to make contact with a man who had fled police and locked himself inside an apartment in Pomona.  
The incident began as a police pursuit that ended near the apartment complex when the suspect's car crashed. The suspect ran from his vehicle and was followed by officers on foot.
He went into the apartment complex and barricaded himself inside one of the units. When officers arrived, he fired through a door, fatally shooting Officer Casillas and injuring another officer.  
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