An expert witness has called into question the reliability of DNA analysis RCMP scientists performed on exhibits relating the alleged murder of Lyle and Marie McCann. Defence lawyer Brian Beresh called Dr.
An expert witness has called into question the reliability of DNA analysis RCMP scientists performed on exhibits relating the alleged murder of Lyle and Marie McCann.
Defence lawyer Brian Beresh called Dr. Randell Libby, a well-respected scientist who has published dozens of peer-reviewed scientific papers on topics relating to molecular biology, DNA analysis and population genetics, to give testimony Monday morning.
Prosecutors have presented evidence linking Travis Vader to the McCanns, including a beer can found in the McCanns' Hyundai Tucson SUV and a hat with a bullet hole belonging to Lyle McCann.
While Libby had not spoken of specific police exhibits prior to the lunch break, he gave general testimony about the limitations of forensic DNA analysis.
Among the issues he addressed are issues Beresh raised in cross-examining the Crown's DNA witnesses, with specific reference to a review of the literature published in a peer-reviewed scientific journal in 2013.
He said it was impossible to tell if DNA is deposited as a result of a single touch or habitual touching, or to tell if the highest-quality DNA sample on an object came from the person who touched it most recently.
Libby also said one can't know with certainty whether DNA was deposited directly or whether it was deposited via a secondary method, or even whether it has been contaminated by any other source – an aerosolized source like a sneeze, for example.
“Neither quantity nor quality of DNA can be used to infer the mode of transfer,” he said.
Furthermore, he said that kind if secondary transfer has been known to happen at crime scenes and laboratories where an investigator or laboratory worker touches two exhibits with the same glove, for example.
“It could happen very easily in a laboratory without the knowledge of the analyst,” he said.
While Crown prosecutor Ashley Finlayson had not yet had the opportunity to cross-examine Libby on his evidence prior to this publication, he did question Libby's specific related hands-on experience.
Libby said his personal direct experience with extracting and processing DNA samples was limited in many of the projects he has been involved with.
“Heavens no, that wouldn't be my role,” he said, explaining he would instead be in a position to supervise those who performed those tasks.
Beresh is expected to finish his questions after lunch, then Finlayson will begin his cross-examination.
Last Friday afternoon, a defence witness testified Vader was ill and stayed at her house from July 4 to July 9, 2010, which contradicts the Crown's theory of where Vader was during that period of time.
Esther McKay-Croswell testified she has long taken in youths and young adults who need a place to stay, and both Vader's sister Bobbi Jo and his ex-girlfriend Andrea Saddleback-Sexsmith were staying with her in July 2010.
Court has previously heard Vader arrived at her house in the late evening July 4, but there has been conflicting evidence as to when he left. Prosecutors have provided cell-phone records which include cell tower locations, combined with testimony from several witnesses that place Vader in the Edson area during that same period.
McKay-Croswell testified that while she was busy caring for the half dozen children in the house and doing all the chores during the time she said Vader was there, she checked on him regularly in the various rooms he was staying – one on the second floor and later in the basement.
She described Vader as being “in pretty rough shape at that point” when he arrived July 4, but the specific nature of his illness was never described.
“He appeared to be sick. I wasn't sure why,” she said.
He slept most of the time, McKay-Croswell said, and she saw him sometimes for meals. She added she believed he had gone out into the fenced yard on the property on several occasions, but that he hadn't left the property.
For each day between July 4-9, Beresh asked where Vader was and she replied with variations of “I think he was at the house.”
“It's more than likely I was at the house and he was at the house,” she said of July 8, for example.
McKay-Croswell said Vader left “around lunchtime” July 9.
Under cross-examination she discussed having spent two hours on several of those evenings out of the house looking for her teenaged son, and also that there was a lot of traffic in and out of the house, with more than a dozen people staying there at any given time. Nonetheless, she maintained Vader had been there the whole time and that even if she didn't see people come and go, she could recognize who it was by the sound of footsteps and of the door opening and closing.
McKay-Croswell also testified that Bobbi Jo Vader and Saddleback-Sexsmith were both using drugs at that time. Beresh has previously suggested the testimony of both of those women was unreliable as a result of drug use.