Toronto police are investigating a possible serial killer who targeted gay men.

Bruce McArthur, 66, has been charged in the deaths of two Toronto gay men. He was arrested in January.

On Monday, McArthur, a landscaper, was charged with three additional murders. Toronto police's lead investigator Sergeant Hank Idsinga said that police found the remains of the men “hidden in the bottom of [large] planters” at a property McArthur used for storage.

Idsinga called McArthur an “alleged serial killer.”

Police are scouring some 30 properties in Toronto where McArthur worked for additional clues.

“We believe there are more remains at some of the properties that we're working to recover,” Idsinga said. “We believe there are more [victims], but I have no idea how many more there are going to be.”

At least one of the victims, all of whom were gay men in their 40s and 50s, had a sexual relationship with McArthur, police said.