Special Investigations Unit spokesman Jason Gennaro says an officer who was in the area at the time of the first shooting tried to arrest a man who he believed was involved in the incident.
Gennaro says the man fled, and a second person was shot.
The second person shot, a 43-year-old man, was taken to hospital and pronounced dead.
Ottawa's police watchdog is investigating three shootings, one of which involved an officer.
Gennaro says the officer followed the man believed to be involved in the shootings into a parking garage, where there was a confrontation.
He says several shots were fired, and the man was pronounced dead at the scene.
His name and age have not been released.
No threat to the public
The SIU is automatically called in to investigate reports involving police where there has been death, serious injury or allegations of sexual assault.
Gennaro says the SIU is taking the lead on the investigation, but will work in tandem with the Ottawa police service.
He says he's not aware of a threat to the public.