Gruesome details of a deadly chest wound were divulged in court Monday in the trial of Abel Cedeno, the teen accused of fatally stabbing a classmate.

A doctor from the Office of the Chief Medical Examiner called Matthew McCree's chest wound "gaping and complex." Prosecutors say McCree, 15, and his friend Ariane Laboy were stabbed by Cedeno following a dispute at the Urban Assembly School for Wildlife Conservation in 2017.

Dr. John Hayes testified Monday, saying, "the blade goes into his heart about 2.5 to 3-inches deep ... it opens the chest, which causes the lung to collapse."

Cedeno is now on trial for manslaughter and other charges. His defense lawyers argue he was a victim of bullying because of his sexual orientation.

MORE: Prosecution’s star witness takes stand in Cedeno school stabbing trial | Cedeno to take stand in his own defense in fatal school stabbing trial 

Students who took the stand Monday say Cedeno and McCree went at it after Cedeno was hit by a paper ball in class.

A classmate who broke down on the witness stand testified, saying, "His body looked real weak, like he lost all of the energy in his body."

Matthew Lawlor, who was a dean at the school at the time of the incident, said, "In the distance I saw blood rolling out of the classroom ... from his chest, the blood was projecting out and he collapsed."

Prosecutors plan to call several more students to the stand before resting their case Wednesday.