There was a heightened security presence at a Bronx school Thursday after two students were stabbed, one fatally, by a classmate.

Mayor Bill de Blasio arrived at the school shortly after the NYPD began dropping off metal detecting wands and metal detectors outside P.S. 67.

As News 12 has reported, Abel Cedeno, 18, is accused of stabbing two classmates in the chest with a switchblade knife in a fifth-floor classroom at the Urban Assembly School for Wildlife Conservation on Wednesday, according to police.

First responders brought both victims to St. Barnabas Hospital, where 15-year-old Matthew McCree later died. Police say 16-year-old Ariane Laboy, the second victim, remains in critical condition.

The three students had been arguing for several weeks prior to the incident and the attack may have come in response to bullying, according to NYPD Chief of Detectives Robert Boyce.

After the attack, police say Cedeno walked out of the classroom and surrendered the weapon to a school counselor. He was taken into custody.

Students say Cedeno had barely been in school the past two weeks, claiming that Wednesday's fight stated after a paper ball was thrown at Cedeno. He asked who threw it, and witnesses say McCree got up and took responsibility for throwing the ball. Witnesses say Laboy got up to defend his friend and was also stabbed.

Education officials say it's the first deadly act of violence in a public school in 25 years.

Cedeno faces multiple charges, including murder, attempted murder and manslaughter.