An expert witness at Travis Vader’s murder trial spent the better part of two days explaining how DNA is collected and analyzed.

Vashni Skipper’s testimony – including a lengthy cross-examination from defence lawyer Brian Beresh and a longer-than-usual re-examination from Crown prosecutor Jim Stewart – finished shortly before the lunch break on Friday.

Skipper An was the first of three DNA experts expected to testify at the trial for the murder of elderly St. Albert couple Lyle and Marie McCann, who disappeared on a trip to B.C. in early July, 2010.

She had testified Wednesday and Thursday about the probability that Vader’s DNA was found in the McCanns’ SUV, which was recovered from a field near Edson. Based on her tests, she said the odds someone chosen randomly off the street would have the exact same genetic profile as the DNA found on a beer can and on the centre armrest is one in 3 trillion.

In his cross-examination, Dr. Randell Libby, a DNA expert who is expected to testify later in the trial, assisted Beresh. He picked apart Skipper’s reports in a highly technical discussion that often referred to highly technical topics such as allelic ladders, relative fluorescent units, and electroferrograms.

He suggested, with respect to several of the matches Skipper had reported, that there could be errors of one form or another. He asked her repeatedly if it was possible for various pieces of data to be interpreted in more than one way, and if it was possible for more than one person to have matches on any one specific area of genetic code.

"You have to analyze the profile as whole," she repeatedly replied, further explaining her findings and how she comes to them.

In the beginning half of the cross-examination, Beresh repeatedly told her, "That wasn’t the question I asked," and eventually Justice Denny Thomas had enough.

"I’m tired of that trick, when you say that’s not your questions and get that kind of response," Thomas said.

Beresh continued his cross-examination, asking yes-or-no questions and not appearing to accept her lengthy explanations in response.

"I’m sorry, sir, but the answer is the answer that I just gave you," Skipper told him at one point.

Beresh also suggested that Skipper might have been biased in her conclusions because RCMP had named Travis Vader as a person of interest in the investigation in July, before she did her tests in August.

In his re-examination, Stewart clarified the timeline: Skipper identified DNA samples as belonging to a "Male 2" in July and August, but it wasn’t until September that she identified those samples matched the DNA sample Vader provided to police.

Skipper’s report, along with several photos and printouts, were numbers as exhibits in the trial.

A second DNA expert who also works in the RCMP laboratory in Edmonton, Vivian Mohrbutter, was qualified as an expert with no objection from Beresh and is expected to begin giving her evidence Friday afternoon.

Halfway mark

The trial, which was initially scheduled to wrap up Friday now appears to be only halfway finished.

Court has heard from two-dozen police, expert and civilian witnesses in Travis Vader’s double murder trial, but after several delays and some witness testimony taking much longer than expected, the trial could now last well into May.

Prosecutor Ashley Finlayson said this week the Crown’s evidence could take two to three additional weeks, and Beresh said he would need at least four days to introduce his evidence after that.