A Toronto police officer who fatally shot a man wielding a knife in the city's east end last May acted in self-defence and will, therefore, not be charged, the province's watchdog has said.

"There are no reasonable grounds to conclude that the (officer) comported himself other than within the limits of the criminal law in his dealings with the (man), there is no basis for proceeding with charges in this case," Special Investigations Unit (SIU) Director Joseph Martino wrote in his report into the May 10 shooting at the Shoppers World plaza near Danforth and Victoria Park avenues.

The report released on Thursday provided a timeline of what transpired between the officer and the 40-year-old man that spring afternoon.

FULL REPORT: SIU Concludes Investigation into Man Fatally Shot by Toronto Police Officer

The incident began just after noon when an off-duty paramedic was walking in the parking lot behind the plaza and saw the man, referred to as the complainant in the report, by a kitchen trailer.

"He appeared of unsound mind – he was agitated and speaking to himself. The complainant was also holding a knife and bleeding from lacerations to both arms," the SIU said.

That prompted the paramedic to approach a nearby police officer, referred to a subject officer or SO in the report, who was inside a cruiser parked a short distance away. After being alerted, the officer drove his cruiser and stopped a few metres away from the kitchen trailer.

He got out of his vehicle and shortly saw the man.

"As the SO approached, the complainant stepped out from behind the trailer and confronted the officer with a knife held in his right hand," the SIU said.

The officer drew his gun and yelled to the man, "Put the knife down." The man did not comply and continued to walk towards the officer holding the knife at shoulder level, according to the SIU.

The officer walked backwards, repeatedly shouting at the man to drop the knife. A short time later, the man began to jog, and when he was within six metres, the officer fired his gun twice.

The man was struck in the abdomen and fell forward. Shortly, the officer handcuffed the man and was heard in his body-worn camera, which was submitted to the SIU, saying, "I want to help you man. I want to help you."

With the help of the off-duty paramedic, the officer rendered first aid to the man. He was transported to the hospital, where he died. An autopsy confirmed that the cause of death was "gunshot wounds of abdomen."

SIU Director Martino said the officer's resort to lethal force was within the scope of justification prescribed by the law.

He added that the officer, who refused to be interviewed for the investigation as his right, "acted to defend himself from a knife attack when he shot the (man)."

"The weapon the Complainant was wielding was capable of inflicting grievous bodily harm and death, and the Complainant seemed intent on using it against the SO and had neared to within striking distance of the officer at the time of the shooting," Martino wrote.

The director believes that the officer's use of his firearm was the "only real tactic available in the circumstances."

"The officer had repeatedly directed the Complainant to drop the knife, to no avail. Instead, the Complainant continually advanced on the SO with the knife held at about shoulder height. Now faced with an individual seemingly bent on attack and quickly closing the distance, the SO had a decision to make. He could continue to retreat, hoping to escape the danger zone, or he could decide to take action to stop the Complainant's advance. The former would have placed public safety at risk given the presence of other persons in the area," Martino said.

"Given the exigencies of the situation, what was needed was the immediate stopping power of a firearm. Anything else would have risked a physical engagement with an armed individual were the Complainant not promptly incapacitated by a less-lethal option."