The homicide squad is leading the investigation.
The building is a Toronto Community Housing property, located on the north side of Wellesley, just east of Sherbourne Street.
It's the second time police have investigated a homicide at the building this year.
In January, police were called to the building, at which time a two-year-old girl was found dead. Months later, the child's babysitter was arrested and charged with second-degree murder.
Also this year, a fire broke out in a unit on the 19th floor, sending a woman to hospital.
Four years ago, a six-alarm fire gutted apartments at the building and left more than a dozen people injured. Some residents were unable to return their apartments for months, while repairs were completed.