Police continue to look into McArthur's activities in what they are calling an "unprecedented" investigation that encompasses hundreds of officers and around 30 properties that McArthur worked on, in Toronto and elsewhere in Ontario.
Idsinga said McArthur has now also been charged in the deaths of 58-year-old Majeed Kayhan, 50-year-old Soroush Marmudi and 47-year-old Dean Lisowick.
Kayhan was reported missing in October 2012.
Bruce McArthur, 66, was arrested earlier this month and charged Monday with three additional premeditated murders after human remains were found "hidden in the bottom of (large) planters" at a property that he used for storage, Toronto police's lead investigator Sergeant Hank Idsinga said. Police believe he was murdered between May 2016 and July 2017.
Police discovered the dismembered remains of at least three men in planters behind this home, where McArthur stored his landscaping equipment.
The formal identification of the remains is pending DNA testing.
McArthur was arrested January 18 and charged with the first-degree murders of Selim Esen, 44, who disappeared from the Yonge-Bloor Sts. area on April 14, 2017, and Andrew Kinsman, 49, who vanished from Cabbagetown on June 26, 2017.
"It is unprecedented and draining. He's an alleged serial killer and he's taken some steps to cover his tracks".
"We do believe there are more and I have no idea how many more there are going to be", he added.
Forensic experts have yet to identify the remains, Idsinga said. Police mounted at least two big investigations into the disappearances, but they were loathe to draw connections between the cases. The fate of the other two men has yet to be determined.
Mahmudi was reported missing by his family in Scarborough in August 2015.
In 2013, police said they believed Kayhan's disappearance may be connected to two other missing persons cases, those of Abdulbasir Faizi and Skandaraj Navaratnam. They also said they there might be more victims.
"These remains have not yet been identified", Det.
Members of the LGBTQ community were pushing for answers previous year in light of the disappearances of Esen, 44, and Kinsman, 29.
Esen frequented the Gay Village area and Kensington Market and often had a small plastic suitcase on wheels similar to a carry-on bag, police said.
April 14, 2017 - Selim Esen, 44, is reported missing from the area of Toronto's Yonge and Bloor streets.
Kinsman was reported missing by a neighbor on June 28, 2017.
Idsinga has said McArthur had a sexual relationship with Kinsman.
The men's bodies were not found before the charges were laid, and police were scouring properties associated with McArthur as part of the investigation. Police wouldn't discuss the specifics of what sort of relationship he had with McArthur, if any.