A former Bronx high school dean testified Monday about the moment he saw “blood rolling out” of a classroom after an allegedly bullied teen fatally stabbed a classmate with a switchblade.

“From a distance I saw blood running out of the classroom,” Matthew Lawlor recalled in Bronx Supreme Court at the trial of Abel Cedeno, now 19, who faces manslaughter charges in the death of Matthew McCree.

Lawlor described his desperate efforts to save McCree as he bled to death in the hallway of the now-shuttered Urban Assembly School for Wildlife Conservation in East Tremont in 2017.

He heard screams coming from the room before he saw “blood rolling out of the classroom” and put the school in lockdown. “Matthew McCree stepped outside and from his chest, blood was projecting out and he collapsed against the wall,” he recalled.

Cedeno has claimed self-defense, saying he was subjected to years of homophobic bullying. But prosecutors say Cedeno walked into class with a chip on his shoulder and was looking for an opportunity to use the knife.