VAUGHAN, Ont. -- Provincial police say four historical missing persons cases involving a complex of retirement homes in Ontario's cottage country are now being treated as homicides.

Det.-Insp. Rob Matthews said the former owners of three retirement properties in the central Ontario region of Muskoka are "of interest" in the disappearance of four seniors in the late 90s.

Those owners were previously charged with fraud-related offences, Matthews said in a phone interview, though he would not elaborate.

"They are two different investigations, but they are certainly relevant to each other," said Matthews, "The former owners were charged, but I can't comment because of their current legal status."

Joan Lawrence, who was 77 years old at the time, disappeared in 1998. Between 1997 and 1999, 91-year-old John Semple, 72-year-old John Crofts and 73-year-old Ralph Grant also vanished.

Matthews said all four are believed to be dead, but their remains have not been recovered.

OPP Interim Deputy Commissioner Paul Beesley said the police force has made significant strides in the investigation, but officers hope to solve the case to help bring closure to the seniors' families.

"Our goal is to simply find out what happened to these poor souls," said Beesley.

Matthews said it was the fraud investigation that eventually led him to the missing persons cases.

The retirement homes -- which are no longer operating -- were owned by four siblings who have not co-operated with police during the probe, he said.

He said the two homes and a farmhouse took in vulnerable seniors who no longer had contact with their families in the late '90s, and police regularly received complaints and concerns over how the occupants were treated.

Matthews said investigators learned residents would escape from the retirement homes in the night and go to homeless shelters in Toronto or Ottawa.

He said 16 deaths occurred at the properties, but only 12 were reported to police. While the 12 were deemed not suspicious, the four others are now being treated as homicides, he said.

Police were initially looking into possible fraud regarding Lawrence's benefits in 1998, Matthews said. No charges were laid. Police were also investigating concerns over how the property owners took payments from residents, he said.

He said Lawrence, who was known at the time as "the cat lady," lived in a small shed on the farm property for two years with "too many cats to count" and that the owners charged her $600 a month for rent.

Matthews said he visited the property after someone contacted police, then returned two days later with a health inspector. But he said by then, Lawrence was gone and the shed had been cleared out.

He said investigators now know Lawrence was moved about 600 metres to an abandoned van "where she met her end on that property."

Matthews said police are appealing for former employees of the retirement homes as well as anyone with information on the case to come forward.