The defence team for accused triple killer Ian Bush called its first witnesses Monday afternoon, among them an expert on trace evidence who said he can't give statistical probabilities about how Bush's hair ended up at the crime scene.

Bush is facing three counts of first-degree murder in the June 2007 deaths of retired Tax Court of Canada judge Alban Garon, 77, Garon's 73-year-old wife Raymonde, and their friend and neighbour Marie-Claire Beniskos, 78.

Bush, now 61, was charged in 2015 and has pleaded not guilty.

Raymonde Garon Alban Garon Marie-Claire Beniskos triple homicide June 2007 victims

From left, Raymonde Garon, her husband Alban Garon, and their friend and neighbour Marie-Claire Beniskos were found dead in the Garons' condo in June 2007. (Photo collage by CBC)

Earlier in the trial, the defence team led by Geraldine Castle-Trudel admitted that a body hair belonging to Bush was found in the living room of the Garons' condo, near the bodies of the victims.

Testifying Monday afternoon via a video feed from Canberra, Australia, expert James Robertson told court during examination-in-chief by Castle-Trudel that it's "just not possible" to talk about the probabilities of hair being transferred from one place to another.

He also testified that evidence gatherers should be very careful about how they pick up hairs, and that anyone who enters a crime scene could potentially disturb evidence — unless they are completely protected.

Limited research on hair transfer

During cross-examination by Crown attorney James Cavanagh, Robertson testified it would take "some degree of force, probably," to remove a person's body hair while it was still growing, and "less so" for a hair in the intermediate stage just after it had stopped growing.

Robertson also told court common sense dictates that the more contact takes place between the body and something else, the more friction there is, and the more forceful that contact is, the more likely it is that growing hairs would be lost.

Geraldine Castle-Trudel lawyer Ian Bush Feb 16 2015

Defence lawyer Geraldine Castle-Trudel. (CBC News)

Asked specifically by Cavanagh about a scenario involving a violent struggle with three victims taking place over a period of time in a confined space, Robertson testified it would provide a "strong opportunity" for hairs to be lost.

When asked about how hairs are transferred from a person's body to something else, Robertson told court there is limited research on the subject, and that determining how something is transferred depends on very specific circumstances.

He also testified that, "all things being equal," the most likely explanation for why a hair would be found somewhere is by direct transfer. The more possible transfers there are and the more complex the scenario becomes, the more assumptions have to be made, he said.

Cross examination gets heated

Cross-examination became heated when Robertson questioned the Centre of Forensic Science's "limited hair examination protocol," and the lack of information about several other hairs gathered from the scene.

Cavanagh asked whether the defence had given Robertson reports presented by Crown witnesses Christine McCarthy, a hair and fibre expert, and Brian Peck, the lead forensic biologist in the case. Robertson said he was asked only to answer 12 questions put to him by the defence, and that he hadn't been provided with full reports.

Cavanagh asked whether Robertson thought it was appropriate to criticize the work of forensic scientists. Robertson told court that, based on the information he was was provided, more could have been done to examine the hairs that weren't suitable for DNA analysis.

Cavanagh then asked about the DNA results from a sample of mixed blood also found near the bodies. The results showed that Bush and a Toronto man who was eliminated as a suspect couldn't be excluded as the source of the blood.

Robertson testified he was made aware of that blood sample but didn't mention it in his report because he's not a DNA expert. 

Samples of mixed blood are "highly contentious," he added, and should be left for DNA experts to discuss.

If the jury finds that it contained Bush's DNA, then an explanation would need to be given as to how the hair and the DNA could have coincidentally ended up in the same place, he told court after a question by Cavanagh.

Engineer testifies about possible balcony exit

Jonathan Parraga, a structural and civil engineer, was called by the defence earlier Monday to give various measurements of the balconies at 1510 Riverside Dr., and the distance between them. 

The balconies are made of concrete, with a glass panel above the concrete and an aluminum guardrail on top of the glass.

The reason for the measurement analysis requested by Bush's defence wasn't revealed until cross-examination, when Cavanagh asked several questions about how someone might get from the Garons' balcony onto the balcony below.

Parraga made it clear several times that he was asked not to speculate, and that whether someone could get from one balcony to the other fell outside his area of expertise. However, he did testify it was 2,150 mm (2.15 m) from the top of the concrete portion of the guard wall to the top of the aluminum guardrail on the balcony below.

He told court it would be fair to characterize the concrete edge as less secure to hold onto than the aluminum guardrail, that if someone was holding onto the concrete their arms would be further away from the building than their feet on the guardrail below — and that anyone going over the wall would be playing with their life.

Parraga also testified that not only would someone scaling the balconies would draw more attention to themselves than if they left by a regular route, but it would also be much more dangerous.

DNA expert to testify

On Tuesday, the defence is expected to call a DNA expert to discuss the results of tests on the smear of mixed blood found in the Garons' condo.

Earlier, court heard that not long after the killings, DNA testing showed a Toronto man couldn't be excluded as the source of some of the blood. The probability that a randomly selected person unrelated to the man would coincidentally share the same DNA was estimated to be one in 13,000.

Years later, after police executed a warrant for a sample of Bush's blood in 2015, the smear of blood from the scene was tested again. It showed Bush also couldn't be excluded as the source, giving the same rate of probability: one in 13,000.

The Crown's case took about a month to present and wrapped last Thursday.