TORONTO -- Investigators working on the case of alleged serial killer Bruce McArthur released a photo of a dead man Monday, a rare move Toronto police hope will help identify someone they believe to be another victim of the 66-year-old landscaper facing six murder charges.

The photo -- a headshot of a bearded middle-aged man with his eyes partially shut -- was released at a news conference where the lead detective announced police had found the remains of a seventh individual linked to McArthur.

Det. Sgt. Hank Idsinga said investigators believe the man was dead when the picture was taken, but refused to say when or how they obtained the photograph.

"I do not want to release this picture and am doing so as a last resort," said Idsinga. "It's obviously a key piece of evidence that we have that we are releasing, but we do feel that by releasing we will identify him and close off that area of investigation."

Idsinga said the photo was released after police exhausted all other avenues to identify the man.

"I would also ask the media to be mindful that by broadcasting this picture a family member or friend not realizing that their loved one is deceased may come to that realization the moment they view that picture ... we need to put a name to his face and bring closure to this man's loved ones."

All six men allegedly killed by McArthur had disappeared from Toronto's gay village or had ties to the city's LGBTQ community.

Idsinga said the latest unidentified remains were recovered from a planter at a Toronto property where McArthur worked as a landscaper and where the remains of the six alleged victims had been found.

Investigators didn't initially realize they had seven sets of remains in their possession, he said.

"I can't really get into specifics about why we didn't realize there were seven remains there, but we had the planters several weeks ago," Idsinga said.

McArthur was arrested in January and charged with the murders of Andrew Kinsman and Selim Esen, who went missing from Toronto's gay village in 2017. Later that month, McArthur was charged with the first-degree murder of Majeed Kayhan, Soroush Mahmudi, and Dean Lisowick. In February, he was also charged in the death of Skandaraj Navaratnam.

Idsinga said there was evidence pointing to a cause of death in at least some of the cases, but wouldn't elaborate.

So far, police have only identified three of the sets of remains recovered -- those of Kinsman, 49, Mahmudi, 50, and Navaratnam, 40.

"We still have four sets of unidentified remains," Idsinga said. "We've gone through fingerprints and dental records and we're now into the DNA process."

The detective was joined at the news conference by Dr. Michael Pollanen, the chief forensic pathologist for the province, to explain the scope of the investigation.

"This is a unique investigation in the history of our organization," Pollanen said. "It is drawing on the talents and expertise of essentially everyone in the organization."

He said the forensic work has been challenging as they examine dismembered remains that were in various stages of decomposition when found in the planters.

"We have technical issues related to decomposition and the effects of post-mortem dismemberment," Pollanen said. "Those are the things we are working through scientifically."

But top of mind for his team is closure for the families of missing persons.

"There is an overwhelming humanitarian objective to identify the people who in this case have gone missing and have been found dismembered and decomposed," Pollanen said.

McArthur's next court hearing is set for March 14.