TORONTO -- Ontario's police watchdog cleared an officer of wrongdoing Tuesday in the shooting of a 51-year-old man who allegedly shot a lawyer in downtown Toronto last year.

In announcing that no charges would be laid against the Halton regional police officer, the Special Investigations Unit detailed the circumstances around the incident that took place in September 2016.

Undercover Halton regional police officers had been following Grayson Delong, who was a suspect in several robberies in Burlington, Ont., the SIU said in a release.

On Sept. 20, 2016, the officers shadowed Delong to the downtown Toronto area, where he parked his vehicle and allegedly got out wearing a reflective construction vest and a blond wig and sat in a nearby park, the SIU said.

The agency said the officers -- suspecting Delong was preparing to commit a robbery -- contacted other area police services to see if Delong matched descriptions of any wanted people, but he didn't.

The man then drove to another area and an officer watched him from the stairwell of a nearby building, the SIU said.

The agency said Delong then suddenly left his vehicle, ran up behind a man, allegedly shot him with a semi-automatic pistol and returned to his car.

After hearing "gunshots, followed by shouting and screaming," the SIU said the officer allegedly saw Delong get into his car. The officer then walked behind the vehicle pointing his firearm at it, yelling "police, police, police!"

As the suspect allegedly drove away, the officer fired three times, hitting Delong twice, the SIU said.

Delong, who allegedly shot criminal defence lawyer J. Randall Barrs several times in the legs outside his law office, faces 15 charges in the incident, including attempted murder, and is set to appear in court on June 9.

Both Delong and Barrs were injured but survived.

"There is no question that the subject officer was acting in the course of his duties when he fired his gun at the fleeing Mr. Delong," said SIU director Tony Loparco.

The officer's actions in the circumstances were "reasonable, responsive, measured and thoughtful," Loparco said.

Loparco said he also looked at whether any "inactions, or omissions," by the officers monitoring the suspect could have justified criminal negligence causing bodily harm charges with respect to Barrs' injuries.

"While his activities certainly warranted suspicion, Mr. Delong was not arrestable for any offences prior to (the alleged shooting)," he said.

The SIU is an arm's length agency that investigates reports involving police where there has been death, serious injury or allegations of sexual assault.