10 pounds of pressure: Ballistics expert testifies at manslaughter trial of Chatham-Kent OPP officer

Testimony continued on Wednesday in the trial of an OPP officer charged with manslaughter in the death of a 24-year-old. CTV Windsor’s Michelle Maluske reports.

The manslaughter trial of a Chatham-Kent OPP officer heard testimony from a ballistics expert Wednesday.

Const. Sean O’Rourke, 57, is on trial for manslaughter in the death of Nicholas Grieves, 24.

He was shot and killed by O’Rourke on July 7, 2021, after being pulled over on Highway 401 near Highgate.

Court learned Grieves – and two other passengers in his car – knowingly left the Dutton OnRoute service centre without paying for $40 in gas.

O’Rourke and the OPP Sergeant on duty that night did not pursue Grieves in a chase but rather conducted a “tandem stop” to pull Grieves over.

Sgt. Bradley Cook told the court while he was approaching Grieves’ car, he heard O’Rourke say, “I think my gun went off.”

Cook did not hear the gunshot but Grieves was shot through the right deltoid, armpit area.

The bullet, court learned, travelled across his chest, severing two main arteries to the upper limbs.

The officers – and later paramedics – tried to save Grieves’ life but he was pronounced dead at hospital.

Judy Chin, a ballistics expert from the Centre of Forensic Sciences testified Wednesday.

She was tasked with examining O’Rourke’s gun in late July 2021 and again in December.

Chin told the court she conducted a “trigger pull weight” test on his Glock 9-mm handgun.

Chin said it takes between 9.3 and 10.91 pounds of pressure – an average of 9.926 – for O’Rourkes gun to fire.

“It’s on the heavier side, but also average,” Chin told the judge.

She also told the court the Glock handgun has three safeties: one external and two inside the weapon.

Pulling back on the trigger – she said – would deactivate all three.

On cross-examination, Chin admitted she did not put O’Rourke’s firearm under a microscope to check for damage to the slider or side rails.

It’s not clear if the defence was alluding to O’Rourke’s police-issued gun having damage at the time of the shooting.

Chin also told the court she was not asked to conduct tests on what would happen if the gun was dropped or bumped.

An OPP training officer – Inspector Jason Oxby – also testified Wednesday.

He testified officers are trained to only pull their weapon out if it’s to preserve life or to show mercy to a wounded animal.

They cannot, he said, pull out a firearm simply to execute a vehicle stop.

He noted however officers can’t be told how or when to pull out their handgun because each call is “dynamic.”

Assistant Crown Attorney Jason Nicol closed his case Wednesday.

Defence lawyer Sandy Kehara told the judge he intends to call evidence from some experts.

Also, it’s expected O’Rourke will testify on Thursday.