Canadian police have recovered the remains of a seventh person believed to have been targeted by alleged serial killer Bruce McArthur, the Toronto landscaper accused of burying the remains of his victims in large flower planters on his clients’ properties.

On Monday, police also released a photo of a man thought to be another victim – a bearded, darker-skinned man who they had so far been unable to identify.

“I do not want to release this picture and I’m doing so as a last resort,” Hank Idsinga of the Toronto police service told reporters. “It is obviously a key piece of evidence that we have that we are releasing, but we feel by releasing it, hopefully we can identify him and close off that area of the investigation.”

He refused to detail where the photo was taken and stressed that it was not clear whether the most recent remains found belong to the unidentified man.

The revelation was the latest in an unprecedented investigation that has rocked Canada’s largest city.

In January – months after Toronto’s LGBT community began voicing concerns that a serial killer was targeting men in the city’s Gay Village – police arrested McArthur, 66, linking him to a string of murders that centred mostly on men of South Asian or Middle Eastern descent.

Police began combing through the sites where the self-employed landscaper had worked, eventually finding the dismembered remains of seven people in planters on a property in the north-east part of the city. Searches have been carried out at another 30 sites connected to McArthur and hundreds of missing persons cases dating back decades are also being re-examined.

Police said there was still much more to do. “We are still waiting for warmer weather to revisit some of the sites,” said Idsinga. “There are several addresses that we’re more interested in than others, but we are continuing those searches.”

So far, the remains of three men have been identified; Andrew Kinsman, 49, Soroush Mahmudi, 50, and Skandaraj Navaratnam, 40. Police have charged McArthur with first-degree murder in connection with their deaths, as well as in the presumed deaths of Selim Esen, 44, Majeed Kayhan, 58 and Dean Lisowick.

McArthur is believed to have met his alleged victims through dating apps as well as in the Gay Village. As McArthur – who also worked as a Santa Claus at a Toronto mall in recent Christmas seasons – had travelled for a previous job, police said they have also been in contact with police forces across Canada and overseas.

McArthur has not yet entered a plea. His lawyer did not respond to a request for comment on Monday.

The earliest murder charge laid against McArthur dates back to 2010, sparking questions as to how his alleged actions escaped notice for years. In January, the Alliance for South Asian Aids Prevention called on the Toronto police to review whether the racial or sexual backgrounds of the victims had any impact on the resources dedicated to the investigation.

“We strongly emphasize that racism and homophobia are systemic issues that affect every part of our society,” the organisation noted in an open letter. “A different standard of justice for racialized and LGBTQ+ people is the reality in our city and province.”