Robert William Pickton's DNA was excluded from several items that also held the DNA of his alleged victims, a jury heard Monday.

As Pickton's trial began its 12th week, jurors remained mired in the reams of scientific evidence the Crown is introducing to prove its contention that Pickton is guilty of murdering six women from Vancouver's Downtown Eastside.

The 57-year-old has agreed the remains of the six women were found on his property, but he has denied killing them.

As jurors heard Monday, Pickton's own DNA could not be ruled out as being on some of the genetic material found on an item that also held DNA matching Brenda Wolfe.

David O'Keefe, qualified by the court as an expert in the analysis of DNA, testified how a pair of handcuff keys revealed the presence of Wolfe's DNA and a minor component of male DNA.

"The donor of police exhibit 356, which is the known sample from Robert Pickton, cannot be excluded as a possible contributor," O'Keefe said under questioning from the Crown.

Accused could be excluded: defence

But under cross-examination, defence lawyer Marilyn Sandford suggested it was in fact possible to exclude the accused based on the genetic markers on the items.

"Mr. Pickton is not excluded as a possible contributor of the minor component, however that doesn't necessarily mean he contributed every [genetic] marker that's showing up as minor," said O'Keefe.

But, added O'Keefe, if one were to agree there could only be two people contributing to the mix, Pickton's DNA could be excluded as being on the item.

In a testy exchange between Sandford and O'Keefe, the reporting officer admitted that Pickton's DNA was excluded as being on a match on a jacket and the contents of its pockets that also held the DNA of Andrea Joesbury and tested positive for blood.

The officer didn't note that fact in his report.

O'Keefe explained the challenge of providing information on mixed DNA samples was that the minor amount of DNA often had limited genetic material, making it difficult for meaningful comparisons with known samples.

O'Keefe said it was possible to make the comparisons, but admitted they weren't made in all cases of male DNA being found on objects seized from Pickton's farm.

"A sample indicative of blood from an object seized from Mr. Pickton's trailer, that has the DNA of a missing woman on it," challenged Sandford. "Surely that's one that should be looked at very carefully and fully reported on before this jury."

O'Keefe agreed.

Pickton's DNA was also excluded from a sweater that matched Mona Wilson.

Court also heard how the bucket containing Wilson's remains was swabbed hundreds of times, but only one swab came back with enough DNA for a match to Wilson, and the sample was mixed with someone else.

But the sample was never run against the list of 1,250 DNA samples analysts were using to make potential evidentiary matches.

DNA links expected to be key to trial

In presenting the results of DNA analysis, links are being established between the thousands of items seized from Pickton's farm and their relationship to the case.

None of the reciprocating saw blades seized from a slaughterhouse contained enough DNA material to form a profile and in most cases, didn't contain any human DNA at all.

The pieces of cellophane wrapped around a sex toy fitted on top of a gun only held the DNA of search technicians and police officers.

One of eight pieces of chewing gum seized from the same location matched Pickton and the others were linked to unidentified men.

But items were found with the missing women's genetic profiles.

Three blankets taken from Pickton's motorhome had Wilson's DNA on them.

One blanket also had a hair with Pickton's DNA and another hair belonging to a different man.

Joesbury's DNA was found on a set of earrings in the slaughterhouse, and on a ring.

Pickton is charged with killing Joesbury, Wilson, Wolfe, Georgina Papin, Marnie Frey and Sereena Abostway.

He is expected to stand trial for allegedly murdering 20 other women at a later date.