The shooter, now identified as Robert Charron, was armed with a registered hunting rifle when he entered the daycare Friday morning, police said in a news conference three days after the incident.
He fired several shots but the children weren't his target and none were hurt, though some may have witnessed the violence, they said.
One of the staff members, 38-year-old Neil Galliou, was killed in the attack before Charron took his own life.
Charron was the estranged husband of the daycare director, who had ended their relationship only days before, police said.
Investigators said he doused his ex and her office with flammable liquid but didn't manage to set either on fire.
Police have not determined a motive but said Monday there is no evidence to suggest the existence of a love triangle.
They said a note found in Charron's home may shed some light on his state of mind.
Charron's link to the daycare's director made him "a familiar face" at the facility, Police Chief Mario Harel said.
He was also a handyman and would have had easy access to the building.
It's still unclear what happened between Charron and Galliou, an art teacher looking to gain work experience.
A French citizen, Galliou had been in Canada for roughly a year and planned to return to his homeland, where his parents still live, so that he could put his skills to use, Harel said.
Galliou's parents told police "their son loved to work with children and would have done anything to protect them had he been able to," Harel said.
Ballistic tests are underway to determine whether the shotgun is linked to both deaths, which police now say are considered a murder-suicide.
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