"During the altercation, the private security officer discharged his firearm, fatally wounding both men," the police statement said.
Donny Ouimette, 25, and Ryan Hind, 39, both of Toronto, both died, while the security guard injured his hand.
Police have never released an exact sequence of events, nor the security guard's name.
Investigators had access to security footage.
According to the release, homicide detectives conducted an investigation that including consulting senior Crown attorneys.
"It was determined that there would be no reasonable prospect of conviction, therefore no criminal charges will be laid," said the statement.