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The murder trial of Mark Grant, accused in the death of Winnipeg schoolgirl Candace Derksen, moved into the world of DNA science Thursday afternoon.
The 13-year-old froze to death after she was left bound hand and foot in a shed in northeast Winnipeg sometime on or after Nov. 30, 1984, the last day she was seen alive.
Mark Edward Grant, 47, has pleaded not guilty to a charge of first-degree murder. Derksen's body wasn't found until Jan. 17, 1985.
More than 20 years passed before Grant was arrested and charged, and much of the Crown's case revolves around advances in DNA science made after Derksen's death.
After almost two weeks of testimony, that science finally walked into the courtroom in the person of Pamela Dixon, an RCMP DNA analyst from Ottawa.
She explained how she received a package in 2001 of items from the 1985 crime scene, including tubes containing samples of the twine used to bind Derksen.
DNA extracted, quantified, amplified
Dixon went through the stages of extraction, quantification and amplification to produce results that she then forwarded to another scientist to interpret and prepare a report. The DNA samples she extracted were incredibly tiny, she told the court, and measured in nanograms [a nanogram is one-billionth of a gram].
By the time she was finished the amplification process, which essentially makes many copies of specific areas in a DNA sample, she had used up most of the DNA she managed to take from the seven segments of twine she was sent.
"In forensics there are nine specific areas that are looked at [in DNA]," she said. "We make . . . millions of copies of that one fragment so it's more easy to be seen."
Crown attorney Brian Bell is expected to call the scientist who reported on the results of Dixon's work to testify Friday.
As he has throughout the trial, defence lawyer Saul Simmonds focused in his cross-examination Thursday on the many ways DNA and other forensic samples can be contaminated.
The people who handled the evidence back in 1985 took few if any of the precautions Dixon said would be taken today to avoid contaminating samples at a crime scene.
But she also said that if additional DNA did show up through testing it would be clear from the results.
