Lecent Ross was shot in a home on Jamestown Crescent, near Martin Grove Road and Finch Avenue West in the city's northwest end, on Thursday morning.
Ross was shot in the upper body, according to police. Police and paramedics were called to the scene around 10:30 a.m. and the girl was raced to a trauma centre shortly after. She was pronounced dead later that morning.
Det. Rich Petrie told reporters on Thursday that the fatal gunshot came from an an "illegal, prohibited, semi-automatic handgun."
Petrie described Ross as "innocent" and the death as "suspicious."
Police will be releasing the results of an autopsy later today.