According to Det. Sgt. Joanne Rudnick, a man followed the 52-year-old victim into the elevator of the apartment building.
Rudnick said the man, armed with a gun, directed the woman to exit the elevator and forced her into a nearby stairwell where she was sexually assaulted.
Police said following the assault, the man fled the building through the front lobby. A surveillance camera set up in the lobby captured an image of a suspect leaving the premises.
The victim was transported to hospital for treatment where she was later released.
On April 19, Rudnick said police were in the Bloor Street East and Parliament Street area when they saw a man who fit the description of the suspect in the alleged sexual assault.
Police said they approached the suspect and spoke with him briefly before they arrested him.
Kyle Michael Junior Young, of no fixed address, was arrested and charged with several offences including sex assault with a firearm, pointing a firearm, uttering threats and carrying a concealed weapon. None of the charges have been proven in court.
Rudnick said that due to the fact that the victim did not know her alleged attacker, it is possible that there may be other victims who have not yet come forward to authorities.
Rudnick also said that Junior Young was known to police.
The suspect is expected to make an appearance in court for a bail hearing today.
Anyone with information is asked to contact sex crimes investigators at 416-808-7474 or Crime Stoppers at 416-222-8477 (TIPS).