A restrained man was found inside alleged serial killer Bruce McArthur's apartment at the time of his arrest, CBC Toronto has learned.

Sources say that Toronto police officers, who were observing McArthur, saw a man enter his home in Thorncliffe Park on the morning of Jan. 18. They say officers believed the man to be in imminent danger.

When officers forcibly entered the apartment to arrest McArthur, 66, they found the man in restraints.

It is believed he went to the apartment seeking a sexual encounter.

3 men tell police about sex with McArthur

CBC Toronto has also learned that police have conducted three interviews with men who had sex with McArthur.

All three told police they stopped dating him because they were uncomfortable with some of the sex acts.

As of Monday, 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.

On Monday, investigators announced they seized a dozen planters after searching through 30 properties where McArthur may have worked.

CBC Toronto learned on Tuesday that in addition to a property on Mallory Crescent in Leaside, police searched two more properties near Yonge Street and Balmoral Avenue in North Rosedale. Police also confirmed their search extends to properties as far as Peel, York and Durham regions.

After forensic analysis of only two of the planters — both from the Mallory Crescent home — police discovered dismembered skeletal remains belonging to at least three people.

A police officer carries containers outside a house on Mallory Crescent in Toronto where skeletal remains were found. (Chris Young/Canadian Press)

Cadaver dogs are also on the hunt for clues, but they are having issues detecting scents due to the cold weather and frozen ground, the police source explained.

Investigators plan to dig up at least two properties as part of their investigation, including the Mallory Crescent home.

Det.-Sgt. Hank Idsinga, the lead investigator on the case, has called the investigation "unprecedented."

He told CBC Toronto that media attention on McArthur has resulted in a number of tips being submitted to police.