"I've never done this and I do it with great hesitation", Idsinga said.
The police are returning to older, unsolved cases to see if they are linked to the killer.
McArthur, a 66-year-old landscaper, has been charged with six counts of first-degree murder in connection with the deaths of Skandaraj "Skanda" Navaratnam, Andrew Kinsman, Selim Esen, Majeed Kayhan, Soroush Mahmudi, and Dean Lisowick.
Idsinga would not comment on how police obtained the photo or where it was taken. He said that it had been altered slightly to make the photograph sharper and to remove "artifacts" from the background.
Fingerprint and dental analysis has not been successful, police say.
The force used the eraser tool 56 times to clean up the image before releasing it to the public.
"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".
Idsinga announced police have also found the dismembered remains of a seventh victim buried in planters at an East Toronto home where McArthur, 66, worked as a landscaper.
BJP used money, muscle power to win Tripura, says Yechury
The governor added that he had asked Rio, who met him on Sunday, to submit signatures of all the 32 MLAs supporting him by Monday. The BJP won 35 seats in Tripura's state legislature against the CPI (M)'s 16 seats, according to India's Election Commission.
Amazon mulling checking-account like product with big banks
A new checking account service would essentially entrench the Seattle-based company even further into the lives of its customers. The retailer would target "young consumers" and people without access to traditional checking accounts, the report says.
TODAY'S FORECAST: Snow, high near 35
The lack of early snow accumulation had many doubting that a major winter storm was underway - if social media is any indication. As an area of low pressure over the Great Lakes dives southeastward, it'll bring snow across parts of Western New York.