A 49-year-old nursing home worker in Ontario has been charged with eight counts of first-degree murder spanning several years.Elizabeth Tracey Mae Wettlaufer of Woodstock, Ontario, appeared in court on Tuesday morning.
The victims were residents in two long-term care facilities where Ms Wettlaufer worked and were between 75 and 96 years old.
Police said seven of the victims were given a fatal dose of a drug.
The victims were residents of Caressant Care in Woodstock and Meadow Park in London, Ontario.
Caressant spokesman Lee Griffi said the accused was a registered nurse and left their employment approximately two and a half years ago.
"We deeply regret the additional grief and stress this is imposing on the families involved," Mr Griffi said in a written statement.
The deaths took place between 2007 and 2014.
Police revealed little details about the motive or circumstances surrounding the deaths in a press conference held on Tuesday morning, but said that the investigation into all eight deaths started on 29 September after police in Woodstock received certain information.
"The information came to our attention, and unfortunately the manner in which it came to our attention will form part of the evidence and we can't speak to that," said Woodstock Police Chief Bill Renton.
The investigation was a joint effort between Woodstock Police Service, London Police Service and the Ontario Provincial Police.
Police said they do not know if there are other victims, but that the nurse worked in other facilities. They are urging the public to come forward if they have any information.