One of the top doctors at the Centre for Addiction and Mental Health (CAMH) defended the institution's system of community access on Thursday after three residents went missing this month.

"The rate [of patients walking away] has varied up and down and we've done a number of things to reduce the rate at which that occurs," said Dr. Sandy Simpson, chief of forensic psychiatry at CAMH.

"This year, it averages about once every 10 days to two weeks. Most of those are somebody coming back a little late from pass," he told CBC Radio's Metro Morning.

Simpson said that while the hospital is accustomed to "there being periods where people are away," the latest incidents give cause for concern.

Zhebin Cong, 47, was found not criminally responsible (NCR) for a 2014 fatal stabbing. He walked away from CAMH on July 3 and then boarded an international flight the same day. His whereabouts remains unknown.

On July 22, Ahmed Sualim briefly walked off the property before being located in Toronto's west end several hours later. The 27-year-old was also found NCR for a string of armed robberies in 2012.

Then on Tuesday, Anthony Murdock, 45, walked away from a supervisor while out on a supervised pass. Murdock was found NCR for a 2002 sexual assault and has a history of other sex-related offences.

Under significant public pressure and calls from both Toronto Mayor John Tory and Ontario Premier Doug Ford for an inquiry into the incidents, CAMH administration announced an external review of its processes around passes and privileges for patients.

Anthony Murdock, 45, was last seen on Tuesday at 2:20 p.m. in the Queen Street W. and Ossington Avenue area, Toronto police said. (Toronto Police Service)

Murdock needs to be in treatment

Murdock was captured on surveillance cameras not far away from CAMH shortly after he walked off, according to Toronto police. The force issued a statement alerting the public to his disappearance, and he remains at large.

Simpson said while an assessment would have found that Murdock did not pose an immediate risk to others, he agreed with the police's decision to warn residents.

Murdock was receiving "treatment for his major mental illness," he said.

"We're concerned about his being at liberty. Our risk assessments are obviously on the basis of him being under care. The longer somebody is not under our care, the more we get concerned about that."

Tory reiterates call for independent review

In a statement following Murdock's disappearance, Tory said it raises further questions about how CAMH and other health-care providers, along with the justice system, work to ensure wider community safety.

"Earlier this month, I was clear that an overall independent review ... should be launched," he said.

"This could simply take the form of having one individual review all of the reports and recommendations expected to be forthcoming to make sure every aspect has been covered given the number of organizations involved."

Tory said Toronto police are currently conducting two reviews in the wake of the Cong case, and CAMH has also committed to undertaking an external review.

The mayor said he's confident that Toronto police are doing everything possible to find Murdock.