MISSISSAUGA, Ont. -- A Hamilton police officer is under investigation in relation to December's fatal shooting of a man hailed as a Good Samaritan, Ontario's police watchdog said on Friday.

Given allegations at the time about how first responders, including police, had acted, the Special Investigations Unit said it had been assessing whether to invoke its mandate.

"Based on the results of those preliminary inquiries, which included medical evidence, the SIU can confirm that it is investigating the role of one Hamilton Police Service officer in relation to this incident," the agency said in a release.

Yosif Al-Hasnawi, 19, was shot trying to help an older man, who had been accosted outside his mosque by two other men.

Two Hamilton paramedics face criminal charges over how they responded to the dying man's pleas for help. Their union subsequently said they had been fired.

Witnesses alleged the paramedics accused Al-Hasnawi of exaggerating his injuries and took too long to treat him and take him to hospital.

Hamilton police charged one man with second-degree murder and another with accessory after the fact in relation to the shooting shortly after the incident. Niagara regional police were then called in to investigate the way paramedics handled the case.

Their union said paramedics Chris Marchant, 29, and Steve Snively, 53, were fired earlier this month, a week after being charged with failure to provide the necessaries of life.

Both were released after their arrests and are to appear in court next month.

Al-Hasnawi's father and two brothers filed a still unproven civil lawsuit in January against Hamilton's paramedics, alleging they failed to treat their relative properly and that his death had caused the family extreme distress. Among others, the suit also named Hamilton police and the two men charged with shooting him.

Police described Al-Hasnawi as a brave young man who had been trying to do the right thing.

Hamilton police referred questions to the SIU, the arm's-length agency that investigates police involvement in death, serious injury or alleged sexual assaults.