NEW WESTMINSTER - Bloodstains found in Robert Pickton's trailer don't indicate the grisly scene Crown prosecutors have suggested and instead could show that small stains had built up over time, a defence witness testified Tuesday.

A now-retired RCMP investigator has testified for the Crown that the accused serial killer's trailer was the scene of a "fatal, blood-shedding event."

But Jon Nordby told defence lawyer Marilyn Sandford on Tuesday that even if he was to assume that a large stain on the mattress was blood, the stain isn't "supportive of a major blood-letting event."

He testified he couldn't conclude for certain that a death had occurred.

While there are many stains that are linked to Mona Wilson inside the motorhome, Nordby said they are all "small stains" and there is nothing to indicate that the stains came from one event.

"They could occur over time," he testified.

Pickton is standing trial in the deaths of Wilson and five others. A trial on a further 20 charges is to be held later.

Nordby conceded many of the stains in the motorhome were linked through DNA testing to Wilson, while many others showed no DNA profile.

Retired RCMP Staff Sgt. Jack Mellis told court earlier in the trial that a large soak stain in the mattress was an indication of a major blood-letting.

But Nordby said assuming the stain is blood, "it doesn't take a lot of blood to cover that area."

"I wouldn't think a great volume of blood was shed over that mattress."

But Nordby, the defence's 26th witness, said there was no DNA obtained from the area and he would have liked to have had the opportunity to closely examine the mattress -- not a photograph -- "to make sure it's blood and not something else."

"Whatever the (mattress) stain represents it could be multiple components," he said. "I can't rule out multiple components on the surface."

Sandford also took jurors and Nordby through an hours-long photographic tour of the motorhome.

But Nordby was critical of the photos taken by Mellis as well as Mellis's conclusions.

Nordby has advanced degrees in philosophy but was qualified by the court as an expert in crime-scene examination and reconstruction, as well as bloodstain pattern analysis.

He delivered a PowerPoint demonstration to the jury in which he was asked about numerous areas in the motorhome on Pickton's property in Port Coquitlam.

The jury has already heard that more than one person lived in the vehicle at various times.

Nordby said repeatedly he was unable to reach a conclusion about several photos Sandford showed him or that the poor quality of the photo inhibited his giving a thoughtful response.

Besides the mattress, Mellis had testified about bloodstains on the carpet, the walls, the corridor and on objects between the two sleeping areas at the rear of the motorhome, including a fridge and stove.

Mellis had also suggested that a body was dragged through the vehicle.

Sandford noted Mellis had testified that some stains on the floor, the fridge and stove were indicative of a body being dragged from the rear to the front of the motorhome.

But Nordby said his opinion of the staining led him to conclude it wasn't necessarily a body being dragged.

"It could be a bloody object."

Pickton is charged with first-degree murder in the deaths of Wilson, Georgina Papin, Brenda Wolfe, Sereena Abotsway, Marnie Frey and Andrea Joesbury.