An 18-year-old Bronx teenager has been charged with murder and attempted murder in connection with a fatal stabbing of a fellow classmate inside of a Bronx high school classroom on Wednesday morning. Another student was seriously injured.

Suspect Abel Cedeno told police that both victims bullied him at the Urban Assembly School for Wildlife Conservation, according to a spokesperson for the NYPD.

Cedeno is set to be arraigned Thursday morning in the Bronx. He has preliminarily been charged with one count of murder, two counts of of attempted murder, one count of manslaughter, one count of attempted manslaughter, two counts of assault, and two counts of criminal possession of a weapon.

15-year-old Matthew McCree died from stab wounds to the chest Wednesday—the first fatality on public school property in New York City since 1993, according to the NY Post. A 16-year-old, who was also stabbed in the chest, allegedly with Cedeno's three-inch switchblade, remains hospitalized in stable condition.

"We believe that this argument has been going on for maybe two weeks, and it escalated today after some back-and-forth into the classroom," Chief of Detectives Robert Boyce told reporters on Wednesday.

Friends of Cedeno also said that the teenager was frequently harassed.

"He usually gets bullied a lot. He's nice. He's sensitive. He has a good heart," 18-year-old Asia Jones told DNAInfo.

"He likes Nicki Minaj," she added. "He'd wear stuff from H&M. He likes Kylie Jenner, that sort of stuff. He would be in the hallways. They would bother him in the hallways, talk crap to him."

Cedeno's friend Yanique Heatley described the two victims as "the school bad boys," adding, "They disrespected teachers. They'd throw trash cans, textbooks, markers. They skipped school."

"They were harassing him and that's when he did what he did," another friend, Tanaisha B., told the NY Post.

The fatal fight broke out half an hour into a third period history class at Urban Assembly, at 2024 Mohegan Avenue in West Farms, according to a preliminary NYPD investigation. The school did not have metal detectors, though wands and detectors were brought in Thursday morning for random screenings.

Cedeno allegedly stabbed both teenagers in the chest around 10:48 a.m. with the three-inch switchblade before walking out of the classroom. The blade was recovered by a school counselor. There were between 15 and 20 students in the classroom at the time of the stabbing, according to police.

The school building also contains the elementary school, P.S. 67.

"I have been a staunch opponent of age-inappropriate co-locations throughout my tenure as borough president," said Bronx Borough President Ruben Diaz in a statement. "High school students should not be in the same building as kindergarteners, period."

Diaz also condemned the "scourge of bullying," adding, "we must do a better job of training school staff to recognize the signs of bullying in order to intervene, long before the situation spirals violently out of control."

"I'm heartbroken at the loss of one of our students and this tragedy should never have taken place," said Schools Chancellor Carmen Fariña. "We are working closely with the NYPD on the investigation and providing ongoing guidance support and counseling for the school community."

Grief counselors are on hand at the campus Thursday.

A woman named Lola Alvarez recorded a live Facebook video at the school after the stabbing, where anxious parents gathered. According to the video, parents were barred from entering the school, where students were held in classrooms.

"There's absolutely no safety here," Alvarez says. "This is chaotic... For all of you politicians, we need you. We need help here in District 12."