Police had been concentrating on 22 potential identifications last week, but Kanagaratnam was not on the list, Idsinga said.
Police were able to identify Kanagaratnam after taking what Idsinga called a "last resort" and releasing a photo where he appeared to be dead.
With the exception of Kayhan, police say they've identified the remains of those men in the planters.
The new charge is for the death of Kirushna Kumar Kanagaratnam, who arrived in Canada from Sri Lanka in 2010.
Idsinga said more remains might be found at the home McArthur used as storage and that 75 properties linked to the landscaper are under investigation.
Surat rape and murder of minor: Police transfer case to CBI
The police are now scanning the list of the missing persons to establish girl's identity and to find out details about her family. The autopsy report also showed that there were severe injuries to the private parts of the girl.
The exact cause of death has also not been determined at this point.
"I think we've all seen in the media so-called experts who tell us that serial killers don't start in their late fifties", Idsinga says.
A 66-year-old landscaper who was known in Toronto's Gay Village, Mr. McArthur was arrested in January, confirming years of community fears that a string of gay men who went missing in Toronto were victims of foul play.
Idsinga said investigators are looking into 15 other cold cases dating back to the 1975, but have not found a connection.
During this time, McArthur allegedly murdered Mahmudi, a man who lived in Scarborough with his wife and hadn't come out to his family; Dean Lisowick, a sex worker who struggled with homelessness, and Selim Esen, a recent immigrant with few friends. He is alleged to have killed them between 2010 and 2017.
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Although police initially said they found the remains of eight people, Idsinga could not definitely say if, between the various body parts found in the planters, the remains of other victims not yet identified were mixed in.
The first probe - named Project Houston - was launched in 2012 to investigate the disappearances of Faizi, Kayhan and Navaratnam.
In this artist's sketch, alleged serial killer Bruce McArthur makes an appearance via video in a Toronto courtroom, on April 11, 2018.
Saunders apologized in February after seeming to suggest in a published interview that police might have cracked the cases earlier if members of the public had been more forthcoming with investigators.
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David Cameron, who was prime minister in 2013, tweeted on Saturday: "As we have seen in the past, inaction has its consequences". May will face questions from MPs on Monday, when parliament reconvenes after a break.