An illegal-drug incident was the “unrelated matter” that had brought police officers to Montreal’s Dawson College just as a gunman began a shooting rampage in September, the Canadian Press reported. A pair of police officers were responding to a call from college security guards, who had detained two students on suspicion of possession of hashish, and the officers ran into the building just after the shooting began, the news service said. The officers’ quick intervention is credited with limiting the carnage, in which one student was killed and 20 other people were injured.

The students involved in the drug incident, who were identified only by the pseudonyms Sean and Albert, have mixed feelings about their role in the tragedy, but praised the unarmed security guard who had detained them, saying he also helped save lives.