Sometime after 4 p.m. on December 6, 1989, Marc Lépine arrived at the building housing the École Polytechnique, an engineering school affiliated with the Université de Montréal, armed with a semi-automatic rifle and a hunting knife.[1] He had purchased the Sturm, Ruger brand rifle, Mini-14 model, on November 21, 1989 in a Montreal hunting store, telling the clerk that he was going to use it to hunt small game. Lépine was familiar with the layout of the building since he had been in and around the École Polytechnique at least seven times in the weeks leading up to the event.

He entered at first in a second floor mechanical engineering class of about sixty students. He asked everyone to stop everything and ordered the women and men to opposite sides of the classroom. No one moved at first, believing it to be a joke until he fired a shot into the ceiling.
Lépine then separated the nine women from the approximately fifty men and ordered the men to leave. He answered: “I am fighting feminism” and “I hate feminists”. He then opened fire on the students from left to right, killing six, and wounding three others.

Lépine continued into the second floor corridor and wounded three students. He shot and killed a woman through the window of the door she had just locked.

He next went down to the first floor cafeteria, and he killed a woman standing near the kitchens. Entering an unlocked storage area at the end of the cafeteria, Lépine shot and killed two more women hiding there.

He entered another classroom where he killed two women. Lépine moved towards some of the female students, wounding three of them and killing another. Moreover, at this point, Maryse Leclair was hurt and asked for help and, Lépine stabbed her three times, killing her. He exclaimed, "Oh shit," and then committed suicide by shooting himself in the head.
He had killed fourteen women in total (twelve engineering students, one nursing student and one employee of the university) and injured