Gunshot residue testing on Tim Bosma's truck revealed that a gun was most likely fired inside the Hamilton man's vehicle, court heard Tuesday.

Robert Gerard, a forensic scientist in the chemistry section of the Centre for Forensic Sciences, told the jury he believes some sort of gun was discharged.

"I've never seen that many [gunshot residue particles] inside a vehicle," Gerard said. "To get that many spread out over such an area in the vehicle speaks to me that a firearm was discharged in the vehicle."

The jury has heard that Bosma disappeared in May 2013 after leaving his home with two men who wanted to test drive a truck he was selling. The Crown alleges he was shot inside his truck.

DNA testing has shown that there is a one in 18 quadrillion chance that blood found on the truck came from anyone other than the slain man.

Dellen Millard, 30, of Toronto, and Mark Smich, 28, of Oakville, Ont., are accused of killing Bosma, 32, who lived in the suburban Ancaster area of Hamilton. Both men have pleaded not guilty to first-degree murder in Ontario Superior Court.

Gunshot residue found in multiple locations

On Tuesday, court saw a diagram that showed 26 gunshot residue particles were found near the driver's seat of the truck on the roof liner, while 35 particles were found near the passenger's seat on the roof liner.

"Thirty-five to me indicates a firearm was discharged very close to that area, or someone had a lot of gunshot residue and rubbed it into the roof. The most likely scenario is a firearm was discharged close to that spot," Gerard said.

'We're looking at microscopic particles that can drift with the air currents.' – Robert Gerard, forensic scientist

Ten particles were also found on the rear passenger side on the roof liner. Two particles were found on the passenger side front dash, one particle was found on the front driver's side door, one was found on the rear door on the driver's side and two were found on the rear passenger side door.

One particle was found on the rear seat on the passenger side, and one particle on the back of the seat on the rear passenger side.

Despite that information, Gerard testified he couldn't say how many shots were fired. "There's no way of knowing," he said.

Gerard also said he couldn't say where the shot was fired from. "You can't really use gunshot residue to determine firing angles. We're looking at microscopic particles that can drift with the air currents," he said.

Defence questions residue distribution

In cross-examination, Millard's lawyer Ravin Pillay asked if activity inside the truck after a shot was fired could affect the distribution of the microscopic gunshot residue particles.

Gerard said yes, if there was lots of movement or wind. "They can be moved about to some extent before … they're deposited on a surface," Gerard said.

"If a vehicle was cleaned, the process of cleaning can affect where gunshot residue particles are found?" Pillay asked. Gerard said yes — it's possible they could be removed or moved around.

In his cross-examination, Smich's lawyer Thomas Dungey presented multiple "hypothetical situations" in which a gun was fired from the driver's seat, including the use of a Walther PPK handgun.

Dungey asked if a secondary source of gunshot residue such as the area where the shell casing is ejected from a gun could account for the 26 particles found on the driver's side roof liner.

"It's really difficult to say from these numbers if that's what we're seeing here," Gerard responded.

Millard's fingerprint matched with photo holding gun

Millard hard drive gun

This photo was found on a computer seized from Dellen Millard's home. The fingerprint was matched with Millard's fingerprint, court heard. (Court exhibit)

Fingerprinting expert Christianne Lys also testified about a photo of a gun that was found on a computer in Millard's home. 

She compared the finger seen in the photo with prints police had on file for Millard and found that they matched.

"There is sufficient quantity and quality of ridge detail in agreement to conclude that the digital image has been identified to the left index finger of Dellen Millard," Lys said.

In cross-examination, Dungey asked Lys if the gun in the photo reads "Walther PPK Cal. 9mm Kurz/380 ACP," referring to his previous hypothesis that a Walther PPK handgun was used in the truck.

Lys said it "appears that way."

Forensic video analyst Michael Plaxton also began testifying Tuesday afternoon about video evidence seized in the case.

The first video the court saw showed a dark-coloured vehicle with no hubcaps going south on Trinity Road around 8:46 p.m. on May 6, 2013.

In another video, a "vehicle consistent with the Bosma vehicle," the report says, was seen going north on Trinity Road at 9:20 p.m., followed by another vehicle.

Overlay shows 'consistencies' between 2 vehicles

The vehicle that followed the truck is consistent with the vehicle in the first video, Plaxton said. It also passed by around the time Bosma left on the test drive, he said.

Reverse projection photogrammetry was used in the case, Plaxton told the court. That means a known object (in this case, Millard's Yukon SUV) is taken back to the scene and re-photographed through the same security camera. "It allows us to overlap those two, and you can now see any differences between the two," Plaxton said.

The investigators brought Millard's SUV back to the area seen in the video in an attempt to do a shot for shot remake with the original security camera video to see if it matched up.

Plaxton's comparison showed that an SUV consistent with Millard's Yukon was following a truck consistent with Bosma's truck.

Plaxton said that despite the consistencies, he doesn't have enough information to say it's definitely Bosma's truck in the video.

A third video was shown in the courtroom that was recovered from Bobcat of Brantford Inc., not far from where Bosma's cellphone was found. It showed a time period from 9:47 p.m. until 10:03 p.m., Plaxton said, when two vehicles are seen approaching and then eventually leaving the area.

CBC reporter Adam Carter is in the courtroom each day reporting live on the trial. You can view a recap of his live blog here:

On mobile and can't see the live blog? View it here.

adam.carter@cbc.ca