Police say the remains were discovered around 11 a.m. Saturday behind an apartment building in the city's north end.
Investigators say the torso is that of a white woman of unknown age and identity.
Police say the woman wore a black T-shirt with the words "Forget princess I want to be a vampire" on the front.
Insp. Kevin Thaler says police want to hear from anyone who may have spotted any suspicious activity in the area.<
"There are people out there that will know what happened here, and why it happened here," Thaler told a news conference.
"We‘ll appeal to anybody with information to come forward and ... give peace of mind to a family at least and identify who this person is."
Police have not recovered any other body parts.
An autopsy is scheduled for Monday in Hamilton.