TORONTO -- A man who killed a Toronto police officer with a snow plow four years ago is being moved from a high-security unit to a lower-security one at the mental health hospital where he's detained.

Richard Kachkar has been at the Ontario Shores mental health hospital in Whitby, Ont., since he was found not criminally responsible for killing Sgt. Ryan Russell.

The Ontario Review Board, which decides if and how NCR patients should be detained, held its second annual review of Kachkar's case earlier this month.

In a decision released this week, it ruled that Kachkar should be transferred from the secure forensic unit of the hospital to the general forensic unit, where patients have more privileges.

The board also allowed Kachkar access to the hospital and grounds while "indirectly supervised," and maintained his access to the general community while accompanied by staff for necessary medical, legal and compassionate needs.

Kachkar has also been granted passes for up to 10 hours to enter the region of Durham while accompanied by staff.

There are three main differences between Ontario Shores' secure forensic unit and its general forensic unit.

The secure unit, which houses patients whose illness is "more acute" and whose risk to the public is greater, has a higher ratio of staff to patients, doesn't allow patients to leave unless accompanied by staff, and has doors that are operated externally by security, said Dr. Karen De Freitas, medical director of the forensic program at Ontario Shores.

The general unit's doors, however, are operated by staff badges and patients can be allowed to leave unaccompanied if their detention conditions permit, she said.

"Patients tend to be more stable, their risk is much less," she said.

The unit is still a secure one though, with patients only allowed to leave with staff's knowledge and permission.

Changes in privileges -- such as indirectly supervised hospital and grounds access Kachkar has gained -- are only granted when a medical team feels a person deserves them, said De Freitas.

"The team has to feel that as a patient your mental state is stable enough," she said. "Your risk has to be low, you've got to be responsible, and you've got to be capable of finding your way around and back."

Patients typically start out with accessing the hospital and grounds for periods of 30 minutes at a time with a call to check in with staff. They have the ability to go up to 12 hours of grounds access with regular check-in periods, said De Freitas. Some patients then progress to gaining indirectly supervised access to the community, she said.

Kachkar stole a snow plow in Toronto in the early morning of Jan. 12, 2011. In the middle of a two-hour rampage, he hit and killed Russell.

Various witnesses heard him yell about the Taliban, Chinese technology and microchips.

Psychiatrists concluded he was psychotic, but struggled with an exact diagnosis.

In March 2013, Kachkar was found not criminally responsible on a charge of first-degree murder.