A Canadian woman who worked as a nurse has been charged with the murders of eight nursing home residents in Ontario over the course of seven years.

If Elizabeth Tracey Mae Wettlaufer is found guilty, The Globe and Mail reports, the 49-year-old woman would be "among the worst serial killers in Canadian history."

"Police say the victims were administered a drug, but they would not provide details about which drug, adding that it is part of evidence that is now before the courts," reporter Dan Karpenchuk tells NPR's Newscast unit. Authorities said the motive is not yet clear.

Police opened their investigation on Sept. 29 and arrested Wettlaufer on Monday. She was formally charged with eight counts of first-degree murder Tuesday at the Ontario Court of Justice and was remanded into custody.

"This investigation is ongoing, therefore I'm not going to speculate whether there will be any additional charges," Woodstock Police Chief William Renton told reporters. "What I can tell you is that we are confident at this time that all of the victims have been identified and that their families have been notified."

Wettlaufer lived in the town of Woodstock, Ontario. Seven of the patients also lived there, at the Caressant Care long-term home, according to police. The eighth patient was a resident at the Meadow Park nursing home in nearby London.

The first victim, 84-year-old James Silcox, died in August 2007, while the most recent victim, 75-year-old Arpad Horvath, died in August 2014. The three men and five women ranged in age from 75 to 96.

The alleged murders have shocked the community in Woodstock. "We're living my father's death right now," Daniel Silcox, son of James Silcox, tells the Globe and Mail. "It's horrific."

Wettlaufer's neighbors described her as a "friendly, unassuming woman" who lived alone with her dog, the CBC reports. The broadcaster says she apparently wrote poems posted on a poetry website that discuss "taking a life" and separately, caring for the elderly.

The case is raising questions within Ontario's Legislature about "how this could have happened in provincially regulated facilities," the Globe and Mail reports. Here's more from the newspaper:

"The coroner's office used to conduct mandatory investigations of every 10th death at a nursing home, but dropped that practice in 2013, in part because the Ministry of Health and Long-Term Care fortified its oversight of nursing homes a few years earlier.

"Since the coroner's office changed its policy in 2013, it has probed far fewer nursing-home deaths. The office conducted 2,027 investigations in long-term-care facilities in 2013. The number plunged to 890 in 2014 and 884 in 2015."

It's not clear whether any of the deaths were investigated at the time they happened. The Toronto Star says Ontario's long-term-care homes have been plagued by controversies and are known to be "severely underfunded and short-staffed."

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