A Canadian nurse was arrested on Tuesday and charged with murdering eight elderly residents under her care at retirement homes in Canada's Ontario province, police said.
The alleged killings occurred between 2007 and 2014 at two private facilities — Caressant Care in Woodstock and Meadow Park in London — where the accused, Elizabeth Wettlaufer, worked.
The 49-year-old faces eight counts of first-degree murder. Wettlaufer appeared in court in the morning and has remained in custody since then.
The male and female victims aged 75 to 96 "were administered a drug," Ontario Provincial Police detective superintendent Dave Truax told a televised press conference.
"We're not in a position at this time to comment further on the specifics of the drug as it forms part of the evidence that is now before the courts," he said.
"All I can offer there is there are obviously a number of drugs that are stored and available in long-term care facilities."
Woodstock Police Chief William Renton said officers began probing the deaths in September after receiving a tip that "a nurse had involvement in the murder of eight elderly patients while she worked at several long-term care facilities in Woodstock and London."
The motive behind the killings is still unknown.
Records from the College of Nurses show Wettlaufer registered as a nurse in 1995 but resigned on September 30, one day after police launched their investigation.
Police said they are not expecting to exhume any of the victims' bodies as part of the probe.
The daughter of one of the victims told local media her mother suffered from Alzheimer's and was in a coma shortly before her death.
Others expressed shock at the news.
A statement from Caressant Care said it is cooperating with police and "deeply regrets the additional grief and stress this (case) is imposing on the families involved."
The criminal case is the largest in Ontario since 2006, when five men were charged with murdering eight biker gang members. They were convicted and sentenced to life in prison.