One of the gunshots that wounded an Ontario police officer during a drug raid this week came from another officer's gun, the province's Special Investigations Unit said Friday.

The police watchdog has determined that at least one of Const. Keith Calderwood's injuries in Wednesday's shootout in central Ontario was caused by a police firearm.

Calderwood, 37, a seven-year veteran of the Peterborough police force, was shot and wounded while executing a drug warrant at a suspected crack house in Lindsay.

Corey Aaron Armstrong, 21, of Morningside Avenue in Toronto, died in Wednesday's shootout but his name was not released until Friday.

A post-mortem was performed Thursday morning.

The SIU, which is investigating the incident, is asking anyone with information about the case to contact the unit.

Four officers from Peterborough Lakefield police have been designated subject officers in Armstrong's shooting. Six officers from Kawartha Lakes police and two from the Peterborough force have been identified as witness officers.

Const. Keith Calderwood, a married father of three, is expected to recover. (Peterborough Lakefield police)

The unit has also assigned a team to investigate the circumstances surrounding Calderwood's injury. Frank Phillips, a spokesman for the SIU, said that investigation is separate from the probe into Armstrong's death.

Calderwood could be out of hospital in a few days

Meanwhile, police say Calderwood could be released from hospital within a few days. The married father of three has been recovering at St. Michael's Hospital in Toronto.

Four of the five people who were arrested during the raid were released Thursday without charges pending further investigation. A Bowmanville, Ont., woman was charged with breach of recognizance.

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.