Tori is evil.
If all she wanted was Cally dead, all she had to do was wait and Cally would have done it to herself - an air-tight suicide.
Instead she played mind games with her and then killed Cally herself. Apparently it was to get Nicky, but it was a very underhanded way of doing it.
And I think the Chief is going to pay Tori back for it at some point in the near future.

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"You miss 100% of the shots you don't take" - Wayne Gretzky