Police spent the night at a Scarborough apartment building after a woman was found dead in one of the units.
Officers were called to Alton Towers Circle, near McCowan and Steeles avenues, at around 11:30 p.m. after receiving a 911 call.
The woman, who is believed to be in her 60s, was pronounced dead at the scene.
Homicide detectives and forensic officers were at the scene Friday morning.
There have been 53 murders in Toronto so far this year.