Legal experts say murder cases without bodies are unusual and it’s even more rare for them to go to trial where prosecutors have an uphill task of proving missing people are really dead.

A trial in Edmonton started this week for Travis Vader, who is charged with first-degree murder in the deaths of two seniors who vanished almost six years ago.

Lyle and Marie McCann, in their late 70s, were last seen fuelling up their motorhome in their hometown of St. Albert, just north of Edmonton, on July 3, 2010. They were setting out for a holiday with family in British Columbia.

They never made it. Their burned-out RV and an SUV they had been towing were discovered in the bush west of the city in the days that followed.

Vader’s defence lawyer has told court there’s not enough evidence to prove the McCanns are dead. A forensic anthropologist testified that he found no human remains in the burned debris from the motorhome.

"It literally has to be proven beyond a reasonable doubt that there has been a death," says a Calgary defence lawyer.

In 1991, Noel O’Brien defended a man charged with murdering his estranged wife. Wilhelmina Wanner was last seen alive in 1989, when blood and hair were found in her bathroom, along with a kitchen knife.

O’Brien says he pointed out alternative explanations to the jury, including that the woman ran off. He didn’t have to prove that she did.

"The Crown didn’t prove she didn’t," he says.

A jury acquitted Jacob Wanner.

O’Brien says there have been convictions in cases with no bodies, but there have been strong motives and circumstantial evidence.

He expects the Crown in the Vader case will call evidence about whether the missing couple used their bank accounts and credit cards after they disappeared and whether the McCanns contacted friends and family.

"How likely is it they wouldn’t have had contact with their children or grandchildren?"

Steven Penney, a law professor at the University of Alberta, says evidence in each case dictates how big of a hurdle it is to prove death. And it would be surprising if Vader’s defence lawyer didn’t raise it as an issue to create some doubt.

Toronto lawyer David Butt was a Crown prosecutor in a no-body case in 2001. Hugh Sinclair, a 72-year-old antique collector, had vanished two years earlier.

Butt says he called dozens of witnesses to testify to show Sinclair didn’t disappear on his own. The man didn’t like to travel or even drive. He kept a regular routine. He had never talked about moving.

Butt says he also had to eliminate the possibilities of accidental death, natural death and suicide.

Court heard Sinclair’s blood was found in his apartment and his DNA was discovered in the trunk of a car rented by a friend, Timothy Culham.

In the end, Butt proved Culham killed the senior to steal his antiques and he was convicted of first-degree murder.

"You have to eliminate all other options … since death isn’t staring you in the face," Butt says.

"You take small, incremental, plausible, logical steps … It’s a way of coming to see what you cannot see with your own eyes."