Cops in Los Angeles gunned down a 19-year-old man who was simply spraying graffiti inside an empty apartment, authorities said.

The unidentified man has been hospitalized in critical condition after being shot Thursday afternoon inside an unoccupied residence in Long Beach, according to the Los Angeles Times.

Police were responding to a call saying several people had been trespassing and tagging the apartment, authorities said.

When the officers arrived, one of them spotted a man inside the residence and opened fire — hitting him with an unknown number of bullets. The 19-year-old was critically wounded.

It is unclear what unfolded immediately before the shooting, but Long Beach police are investigating, authorities said.

The Los Angeles County District Attorney’s Office also will conduct its own probe — a customary procedure in all officer-involved shootings.