Notre-Dame hospital issued a news release at 5:06 p.m. on Wednesday convening journalists immediately for an announcement on "major events," 11 days after the first death.
Those events were the slaying, by suffocation, of two elderly patients in the psychiatric ward. The first death occurred on June 16 and the second was last Thursday.
The third and final incident was an attempted murder, also in the psychiatric ward, on Friday. An arrest was instantly made in that case, although police have not confirmed that all the incidents are linked.
One senior hospital official praised the work of his staff.
"Thanks to the vigilance of the management and our employees, information was given to investigators about two deaths from apparent natural causes in the same period," said Yvan Gendron, the hospital's associate director general.
He said the hospital will conduct a review to see whether any changes are needed, although he said the institution already has strong security measures.
"The events were isolated incidents," he said. Gendron said the news of the deaths was delayed because families were being advised.
Police said they were informed by staff about the deaths when they went to investigate the attempted murder.
"We're talking about two elderly people that died by asphyxiation," said Montreal police Const. Daniel Lacoursiere. He did not connect the suspect in the third incident to the two deaths.
"Following the results of the autopsies of these two deaths, the case was transferred to our homicide squad. Presently concerning the two homicides, there are no arrests and the investigation is presently ongoing."
Lacoursiere was tight-lipped about further details of the deaths: "We're going to keep to ourselves a lot of details because a lot of the family members were not advised."
Police arrested a 31-year-old man for the attempted murder of a fellow patient last Friday, and he has been arraigned.
The suspect has been ordered by the court to undergo a psychiatric evaluation.
The survivor of his alleged attack is a 71-year-old woman.
Gendron said the hospital is co-operating with police. It is also conducting its own internal review.
"If improvements need to be done, we'll do it," he said.
"Rigorous security measures exist at the (hospital). We're proceeding with an examination of all the facts."