A 14-year-old Bronx boy has turned himself in for the murder of an 18-year-old young man in Washington Heights early Saturday. Alvin Diaz is being charged with second-degree murder after police say he fatally stabbed Dereck Cabejas in the chest; the murder was allegedly committed in reaction to a water fight two days earlier.

Cabejas, Diaz and the suspect's brother reportedly fought with water on Thursday, but witnesses tell the Daily News the playfulness devolved into actual fighting on Friday, when Cabejas slapped Diaz, apparently over lingering water-based resentment. "[Diaz] said, 'I'm gonna come back,' " the victim's mom, 34-year-old hospital worker Jenny Cabejas, tells the News. "My son didn't think nothing. You're a little kid! He didn't think this kid was going to come stab him."

Diaz allegedly made good on his pledge, returning to Cabejas's apartment building on Audubon Avenue near West 176th Street around 12:55 a.m. and plunging a kitchen knife into his chest. Cabejas was pronounced dead at Columbia-Presbyterian Hospital.

Before turning himself in, Diaz, who now holds the dubious title of youngest murder suspect in NYC, asked his Facebook friends to visit him in prison. One friend responded, "What you did was wrong, but you learn from it," the News reports. (We were unable to find Diaz's Facebook page to corroborate this; the account may have been removed.) Diaz has no criminal record, but a man who answered the door at his family's Bronx home called him a "great kid."