Investigators comb through sewers for clues to deaths of Barry and Honey Sherman

Forensic investigators are now combing through sewers looking for clues into the deaths ofa billionaireCanadian couple"out of an abundance of caution," a source close to the investigation has told CBC Toronto.

Apotex founder, Barry Sherman, 75, and his wife Honey, 70, were found dead in their North York home on Dec 15.

Investigators could be seen working with city employees Saturdayto open up sewer grates near the house.

The team plans to comb through more sewers near the Sherman's mansion on 50 Old Colony Road, nearBayviewand the 401 as soon as they can coordinate the operation with the city.

The forensics team were assisting homicide detectives who have officially taken the lead in the case although it remains a "suspicious death investigation," rather than a homicide. Post-mortem examinations have revealed that both Shermans died from "ligature neck compressions," meaning strangulation.

Police have remained tight-lipped aboutdetails of the investigations but a detective with the Toronto homicide squad, Brandon Price, previously said investigators found no signs of forced entryinto the couple's house, and police were not "currently seeking or looking for an outstanding suspect."

Mourned by thousands

CBCNews has learned that theShermanswere found by the pool in their basement and that investigators have found no security cameras inside or outside the home.

The Sherman's funeral, held Thursday, was attended by thousands including Prime Minister Justin Trudeau, Ontario Premier Kathleen Wynne, Ontario Health Minister Eric Hoskins and Toronto Mayor John Tory.

Barry Sherman founded Apotex in 1974 and has amassed a vast fortune since. His net worth was recently estimated by Canadian Business magazine at $4.77 billion, making him the 15th richest person in the country.