Passersby spotted the torso floating near the Rainbow Bridge on Wednesday afternoon.
Niagara Falls Insp. Jim Mccaffrey said Friday the woman was a murder victim. Mccaffrey says they've asked police in New York and Ontario to review missing-person files.
Police say the torso is not connected two other dismemberment cases in Canada in recent months. Those two cases were not connected.
In the first case, porn actor Luka Magnotta was accused of dismembering a Chinese student in Montreal and mailing his body parts to political parties and a school.
