Another student was seriously injured.
The melee unfurled at 11:00 a.m. Wednesday morning, about 15 minutes into third period at the Urban Assembly School for Wildlife Conservation, a middle and high school in the Bronx, the New York Police Department said.
The Bronx school was open Thursday. He has been charged with one count each of murder, manslaughter and attempted manslaughter and two counts each of attempted murder, assault and criminal possession of a weapon.
The effort reflects a growing interest in NY and beyond in establishing charter schools that enroll students from a mix of backgrounds, which research suggests can benefit students and is considered one remedy to school segregation. Family members identify 15-year-old Matthew McCree as the teen who died, the other just 16, was critically wounded.
At a news conference with police and school officials, New York City Mayor Bill de Blasio said everyone in the community has been affected by the violence.
Boyce said that with Cedeno's mother stranded in hurricane-ravaged Puerto Rico, police were in contact with his older brother. He's nice. He's sensitive.
Boyce said that the 18-year-old student "has made statements to us explaining what happened".
"He likes Nicki Minaj, stuff from H&M". He'd wear stuff from H&M. "He likes Kylie Jenner", she said.
Mr Cedeno bought the knife online for protection two weeks before the attack and admitted to stabbing the two teenagers with it, assistant district attorney Nancy Borko said in court on Thursday. They'd throw trash cans, textbooks, markers. When Ariane got stabbed they were holding towels on him. Scissors were found at the scene.
When asked if he was picked on, 18-year-old Abel Cedeno replied "yeah" before detectives escorted him into a vehicle ahead of his arraignment expected Thursday. "He was confronted by a counselor in the hallway, where she asked for the knife and recovered the knife".
Matthew McCree, 15, was fatally stabbed at Urban Assembly School for Wildlife Conservation in the Bronx. "I don't know if I want to keep her here", she said.
It was the first slaying inside a city school since February 1993.
Schools Chancellor Carmen Farina added, "Every parent has the right to expect that when they send their children to school in the morning, they'll come back at 3 o'clock in very good shape".
Police said Cedeno had not gone to school officials before with any complaints of harassment.
Grief counselors will also be on hand. According to the video, parents were barred from entering the school, where students were held in classrooms.