The issue of DNA evidence formed the focus of testimony in the Candace Derksen murder trial on Thursday.

Mark Edward Grant has pleaded not guilty to the charge of first-degree murder in the death of 13-year-old Candace Derksen, who disappeared on her way home from school in 1984 and was found dead weeks later in January 1985.

Retired RCMP inspector Donald Ogilvie began testifying Thursday about his extensive experience in 1985 working with the hair and fibers evidence section of the RCMP in Winnipeg.

Last week, the Crown argued that Mark Edward Grant's DNA was found on the twine and said seven of his hairs were found at the crime scene.

Ogilvie testified he was presented with evidence from the shed where Candace Derksen was found during the investigation.

He examined the evidence, including machinery and logs from the shed and items of Derksen's clothing for hair and fibers, mounting the hairs he found on microscope slides.

More than 20 years later, the condition of the slides is very different from how he left them, Ogilvie testified.

Ogilvie said that the sticky material he had used to mount the hairs on the slides had dried out and in some cases, parts of the hairs were sticking out of the slides, with more hairs present than there appeared to be in 1985.

Defence lawyer Saul Simmonds questioned Ogilvie about his handling of the evidence and the possibility of it being contaminated with other DNA material in the lab, or with his own DNA.

Several hairs were recovered from a log in the shed. Simmonds asked Ogilvie about how the log was transferred to the lab.

Ogilvie testified that the log was not packaged when transferred to the lab. When asked by Simmonds, he said he could not say for sure which end of the log was facing up and which end was down on the ground of the shed.

The lab was also in possession of other hairs and pieces of evidence, including material from the Derksen's home, court heard.

Simmonds specifically questioned Ogilvie about a note he had made indicating that the Derksen family had not been ruled out as suspects at the time. Ogilvie testified that was what he was told by police at the time.

The next witness, RCMP analyst Pamela Dixon, testified about examining the twine that Derksen was found bound with in 1985.

Holding tubes containing twine samples in her gloved hands while she testified, Dixon spoke about receiving sections of the twine from Winnipeg police in 2001 to examine.

At an RCMP lab in Ottawa, Dixon put the twine through a process that extracted DNA material from the twine.

Dixon testified about quantifying and "amplifying" the DNA, which she described as chemically copying important sections of the DNA.

Dixon testified that there was enough DNA present to complete each step she took.

Then, a DNA profile was created by a machine and sent to her colleagues to be analyzed.

On Thursday, defence lawyer Simmonds asked Dixon if the quality of her results is only as good as the evidence she receives, saying it is a problem described as "garbage in, garbage out" by other experts in her field. Dixon agreed.

Simmonds also asked Dixon about the potential for contamination of DNA evidence--whether by police officers, analysts or other people. Dixon agreed that contamination can be a problem.

Simmonds asked her about the potential of contaminations from "all of the hands" that had touched the twine over the years.

"The source of the DNA we found would have had to have come from contact at some point," Dixon said.

The murder trial is set to continue in Winnipeg.