04/07/2016 18:01 EDT | Updated 04/08/2017 01:12 EDT

Defence tries to poke holes in DNA evidence at trial of Travis Vader

EDMONTON — The defence lawyer for a man accused of killing two seniors who vanished in the summer of 2010 has cross-examined an RCMP scientist in an effort to poke holes in DNA evidence submitted at the trial.

Vashni Skipper testified Thursday that DNA matching Travis Vader's was found in four places in an SUV belonging to Lyle and Marie McCann.

She said it was on a Boxer beer can, a blood smear on the vehicle's centre console, the steering wheel and in blood on a passenger seat.

Under questioning by defence lawyer Brian Beresh, Skipper agreed that testing can't say when the DNA was put there.

She also agreed there was a possibility that sneezing into a vehicle or onto items might be enough to transfer DNA.

The McCanns were last seen driving their motorhome with their green Hyundai Tucson towed behind it as they set out from St. Albert, a bedroom community north of Edmonton, on July 3, 2010.

The great-grandparents, in their late 70s, were going on a camping trip to meet family in British Columbia.

Two days later their motorhome was found burning in the bush in the Peers area. Their SUV was later found hidden in some trees on a nearby rural property.

Their bodies have never been found.

The Crown alleges Vader was a desperate drug user on the run from police, and living in a makeshift camp in the region, when he came across the McCanns and killed them. The defence has suggested there's not enough evidence to prove the couple is really dead and that police should have looked at other suspects.

Vader, 44, has pleaded not guilty to first-degree murder.

(CTV Edmonton)