RCMP believe Lyle and Marie McCann were killed on the day they vanished more than a year ago, according to court documents.
A court order declaring the Alberta couple dead was granted last week so the family can begin processing wills and dealing with the estate, said the McCann's son, Bret.
A letter from the RCMP said his parents were killed on the day they were seen gassing up their motorhome in their home town of St. Albert, just north of Edmonton, before a trip to British Columbia.
However, the letter gives few details on what police think happened.
"As this is an ongoing criminal investigation and no charges have yet been laid in the matter, the integrity of the evidence must be maintained," said Staff Sgt. Don Campbell.
"It is due to this reason I cannot provide the specifics as how it can be demonstrated that Lyle and Marie McCann were murdered in the Edson area of Alberta on July 3, 2010."
Two days later, the couple's burned-out motorhome was found in a backwoods campground area near Edson, Alta.
An SUV they had been towing was discovered a few days later in heavy bush several kilometres away.
RCMP named a suspect in the case, but have not laid any charges.
The family is holding a memorial service on Saturday on what would have been the couple's 59th wedding anniversary.