Police arrested Elizabeth Tracy Wettlaufer and charged her with eight counts of first-degree murder, police said during news conference in Woodstock, about 140 kilometres southwest of Toronto.

“The homicides occurred at nursing homes in Woodstock and London, in the province of Ontario, between 2007 and 2014,’’ Woodstock police Chief William Renton said.

Renton said that the victims were between the ages of 75 and 96.

Police would not say how the victims died, except that seven were administered a fatal dose of a drug.

Renton told newsmen that the investigation began on Sept. 29, after police were tipped off that a nurse was involved in the murders of eight patients in two long-term care facilities in Woodstock and London.

“While the police investigation is still ongoing, authorities are confident that all the victims have been identified.

“Eight murder charges are the most brought against any individual in Ontario since eight men were killed in a gangland execution in 2006,’’ Renton stressed.