Story highlights Elizabeth Wettlaufer pleaded guilty to poisoning 8 care residents over seven years

She said she thought at first God wanted her to do it

(CNN) A Canadian woman who pleaded guilty Thursday to killing eight assisted-living facility residents while she was a nurse told a detective in a video confession that she thought God wanted to use her.

Elizabeth Tracey Mae Wettlaufer said she injected patients with lethal dosages of insulin when she poisoned residents who ranged in age from 75 to 90 in two Ontario facilities between 2007 and 2014.

According to CNN partner CBC News , Wettlaufer, 49, told an interrogator that she was angry with life.

In the video, played during her one-day trial Thursday, she says she knew the difference between right and wrong. But she said she would get a "red surging with God telling me this is the one."

She also picked some victims because they were "mean," CBC News reported.

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