Cops have identified one of the five people arrested in the mistaken-identity slaying of 15-year-old Lesandro “Junior” Guzman-Feliz.

Kevin J. Alvarez, 19, of the Bronx, was named Sunday night as one of the alleged killers.

He was charged with second-degree murder, manslaughter, gang assault, and assault, according to police.

Authorities would not say which person he was in the surveillance video showing the attack on Guzman-Feliz. The young man was identified as a Parkchester resident. It’s unclear if he surrendered to police or was taken into custody.

Grief-stricken relatives and friends of Guzman-Feliz gathered outside the 48th Precinct on Sunday night — where Alvarez was being held — to voice their outrage over his death. One person shouted obscenities at the young man as he was led out of the police station.

“That was a baby,” railed Janet Zorilla, whose son was friends with Guzman-Feliz. “I hope you rot in jail, motherf—ker! I hate you! I hope you die, bitch!”

Three of the five men who were arrested Sunday were busted in Paterson, NJ, during a raid, according to sources. Another man was said to have walked into the 48th Precinct and turned himself in.

Additional arrests are expected.