The 66-year-old McArthur is already facing murder charges in the deaths of Mahmudi and Kinsman.
Police launch Project Houston to investigate the disappearance of three men from Toronto's gay village, including Navaratnam and Kayhan.
McArthur faces first-degree murder charges in the cases of five men - Andrew Kinsman, 49, Selim Esen, 44, Majeed Kayhan, 58, Soroush Mahmudi, 50, and Dean Lisowick, 47.
Police have only confirmed the identity of one of the victims, Andrew Kinsman.
Homicide Det. Sgt Hank Idsinga had been saying he expected to lay more charges since early February when a probe of an east-end house where McArthur worked as a landscaper and stored his equipment led to the discovery of the body parts of six people buried in planters.
The case has evolved with police now looking at "hundreds of outstanding missing persons occurrences" and even "occurrences where there's been a sudden death". "We do believe we have multiple murder scenes, though", said Idsinga. Navaratnam, 40, was reported missing in 2010 after last being seen leaving the now-defunct Zipperz nightclub in the heart of Toronto's Gay Village.More news: Trump Threatens to Pull Immigration Agents Out of California
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He added that police are tracing McArthur's whereabouts "as far back as we can go".
Police have interviewed some of McArthur's past known associates, but Idsinga said there is no reason to believe that the investigation now involves a hunt for other suspects. This brings to six the number of charges of the capital crime now attributed to the former landscape contractor. There are also "two or three" other properties linked to McArthur that Idsinga said he's "interested" in.
When asked how the two latest victims were identified, Idsinga said they used dental records.
McArthur's next court appearance is scheduled for February 28.
Though police expect to find more victims beyond the human remains in the planters, they say the entire investigation process could "go in to the years".