According to a new report, investigators may have a working theory in the ongoing murder case of billionaires Barry and Honey Sherman.

One of the lead Toronto police detectives handling the Sherman murders told a court on Wednesday that police have “an idea of what happened,” the Toronto Star reported.

Kevin Donovan, the Star’s chief investigative reporter and the journalist who broke the story, told CTV News Channel there’s at least one person who has refused to speak with investigators, but police wouldn’t elaborate on who that person is.

“One speculation I have is that is indeed a suspect, somebody they want to ask questions, who would have material information – perhaps even the person involved and that person’s not speaking,” Donovan said on Thursday.

Donovan also said there are other individuals that police have been unable to locate and there’s a belief that they may have left the country.

The Apotex founder and his wife were found dead in the basement of their home on Dec. 15, 2017. The couple was found in a semi-seated position with belts looped around their necks.

No arrests have been made in the investigation.