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The Crown on Thursday completed its case in the trial of Mark Grant (left), accused in the 1984 death of Winnipeg teen Candace Derksen. ((CBC))

Faulty testing could have led to false DNA conclusions against a man accused of murdering a Winnipeg schoolgirl, court was told Friday.

Genetics professor Dr. John Waye is testifying on behalf of the defense team for Mark Edward Grant, who is charged with first-degree murder for allegedly grabbing Candace Derksen off a Winnipeg street as the 13-year-old walked home from school in November 1984.

She was left hog-tied to freeze to death in a brickyard shed not far from her family's home. Her body wasn't found until the following January.

The crime remained unsolved until work done in 2006 by Molecular World, a private DNA lab in Thunder Bay, Ont., linked Grant to the crime scene.

Waye testified Friday morning that one of the analysts at the lab excluded data that may have led to false conclusions about the DNA results.

'You can't ignore data because it doesn't fit your expectations.'—Dr. John Waye

"There was results that don't fit a scenario of Mr. Grant being a contributor to this [DNA profile]," said Waye, professor in the department of Pathology and Molecular Medicine at McMaster University and head of the Molecular Diagnostic Genetics Service of the Hamilton Regional Laboratory Medicine Program.

"You can't ignore data because it doesn't fit your expectations," he said about the incomplete DNA analysis he believes was done by Molecular World.

No evidence without DNA

DNA tests are at the core of the case against Grant, 47, because tiny amounts of physical evidence, such as broken strands of hair, are all that remain of a crime that gripped Winnipeg a quarter-century ago.

"If Molecular World was wrong, that's all you have," defence lawyer Saul Simmonds said on Thursday, as he cross-examined Patrol Sgt. Allan Bradbury, the head of the cold-case unit who arrested Grant in May 2007.

Bradbury agreed with Simmonds that they had no other physical evidence against Grant and he said nothing to implicate himself when they questioned him.

Grant was questioned by police shortly after Candace's disappearance but wasn't viewed as a suspect at the time. The break in the case came after old evidence was reviewed using new science.

'You got clear answers to clear questions ... 'I didn't do it, whether you believe it or not.'—Mark Edward Grant, in taped interview with police  

But Simmonds noted Thursday that throughout more than 3 ½ hours of videotape from a lengthy police interview, Grant continued to profess his innocence.

"You got clear answers to clear questions ... 'I didn't do it, whether you believe it or not,' " the lawyer put to Bradbury, paraphrasing Grant.

In the videotaped statement Grant says very little, other than denying he had anything to do with Candace's death.

Simmonds said about all police learned was that he likes Mr. Bean movies, comes home from work, cooks dinner and enjoys going for walks.

The man pictured on the tape looks like someone who had spent a lot of time outside — slightly sunburned, with strong, heavily tattooed arms.

The Grant who has sat in the courtroom every day is pale, stout and often dressed in a grey suit and tie.

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The supply shed near the Nairn Overpass where Candace Derksen's frozen body was found on Jan. 17, 1985. ((CBC))

Simmonds has been highly critical throughout the trial of how the DNA evidence was collected.

Standards were a lot looser in the 1980s and he noted little was done to prevent contamination of material found at the crime scene. The DNA came from hairs found on Candace and from the twine used to bind her hands and feet.

The defence also spent a great deal of time attacking the Crown's chief DNA witness, Amarjit Chahal, who Simmonds said excluded some DNA data that might have exonerated Grant when he prepared his report.

Chahal said since the 26-year-old sample he reviewed was degraded, he only used 10 of the 15 markers he would normally check to determine a DNA profile. He suggested there was only a one-in-50-million chance that, when all the DNA evidence was combined, it came from someone other than Grant.

But Simmonds has said if some of the missing data Chahal decided not to compare had been included, it could have excluded Grant as a suspect.

Bradbury said the DNA evidence allowed them to eliminate everyone but Grant, although he conceded they didn't get DNA samples to submit to Molecular World from everyone they might have.

With files from The Canadian Press