While a 16-year-old Long Island boy lay with a fatal stab wound to the chest following a violent brawl Monday night, Sept. 16, about 50 other teenagers stood by instead of helping the boy, some recording his slow death on their phones, the police said.

Police said the fight, involving as many as 50 teens, broke out at a strip mall in Oceanside, New York and was captured on video posted on social media.

“Kids stood here and didn’t help Khaseen — they would rather video this event. They videoed his death instead of helping him,” Nassau County Police Department Detective Lt. Stephen Fitzpatrick said in a press conference Tuesday, adding: “This can’t go on. Your friends are dying while you stand there and video it. That’s egregious.”

Nassau County police said the victim, identified as Khaseen Morris, a senior at Oceanside High School, died of his injuries at the hospital.

Fitzpatrick and Khaseen’s family said the fight appears to have started over a girl, who was not present during the fight. It was a prearranged fist fight after Khaseen was seen with another boy’s girlfriend. He was threatened he better be there, then set upon by six or seven teens from another school district.

Keyanna Morris, 30, Khaseen’s older sister, said a 10th-grade girl asked Khaseen to walk her home.

Morris suspected the girl was trying to make an ex-boyfriend jealous.

The older sister said Khaseen was a “sweet” and “funny” boy who loved drawing, skateboarding, and anime.

Police said 18-year-old Tyler Flach, of Lido Beach, was arrested Wednesday, Sept. 18, in connection with the death of Khaseen Morris.

The suspect was charged with murder. He will be arraigned Thursday in Hempstead.