Toronto landscaper Bruce McArthur now faces three additional counts of first-degree murder, bringing the total to five in what police are calling a serial killing case that the city has never seen before.

Det.-Sgt Hank Idsinga said Monday that investigators have reason to believe McArthur killed Majeed Kayhan, Soroush Mahmudi and Dean Lisowick.

"What kind of case is this?" Idsinga asked rhetorically at a news conference. "It's a serial killer."

'I have no idea how many more there are going to be,' says Det.-Sgt. Hank Idsinga 1:35

Idsinga said there may be even more victims who have yet to be identified.

"We do believe there are more and I have no idea how many more there are going to be."

McArthur, 66, was previously charged with two counts of first-degree murder in the deaths of Selim Esen and Andrew Kinsman, who both disappeared in 2017.

Police say Kayhan went missing in October 2012 and Mahmudi in August 2015. They believe Lisowick was killed in 2016 or 2017.

Remains found in planters

Idsinga said police discovered dismembered remains in the bottom of large planters after searching a property linked to McArthur at Mallory Crescent in midtown Toronto.

"There's at least the remains of three people among those body parts," said Idsinga.

McArthur now faces first-degree murder charges in the deaths of Majeed Kayhan, Soroush Mahmudi and Dean Lisowick, left to right. (Toronto Police Service)

He added that more DNA and other analysis is being done on the remains to determine the exact identities of the victims.

Karen Fraser lived at the Mallory Crescent property with her husband and told CBC's As It Happens McArthur would often store equipment — including large planters like the ones where the body parts were found — on her property in exchange for cutting grass.

McArthur would do more for her, including helping her with charity work, she added.

Toronto police probed a home linked to Bruce McArthur, located on Mallory Crescent in the area of Bayview and Moore avenues. Although McArthur didn't live there, he did landscaping work for the couple who lived at the property and stored equipment there. (Mehrdad Nazarahari/CBC) "He has been kind, helpful, helped with our charity work, doing floral gifts for silent auctions," she said. "He went above and beyond what our original agreement was to cut the grass."

Fraser said she now struggles to fall sleep and thinks about how some of the alleged victims were immigrants.

"I know sometimes they feel incredibly vulnerable. A lot of them are here without family," she said.

"I picture these men, glad to be making friends. They found a community. They really think that their new life is going to be maybe more than they ever dreamed possible — and then that someone took advantage. The terror, the horror — that's what I have real trouble with"

Other sites to be searched

Since McArthur's arrest, police have identified approximately 30 properties where the self-employed landscaper may have worked.

Idsinga said police have searched the majority of the properties, and urged anyone who may have employed McArthur to contact them so they can search the area where he may have worked.

"He's taken some steps to cover his tracks and we have to uncover these victims," Idsinga said.

Investigators have also seized other planters to go through and have identified at least two other sites to be excavated.

Toronto police recovered body parts of 'at least' three victims inside planters at the Mallory Crescent home. (CBC)

'Unprecedented' investigation

Idsinga also confirmed that McArthur was first identified as a suspect in September in connection with Kinsman's disappearance.

Officers arrested him after uncovering evidence that also linked McArthur to Esen's death.

The ensuing investigation has required "unprecedented" resources, police said.

"We've never seen anything quite like this with the number of crime scenes that we have to process," Idsinga said.