A defence lawyer representing Christy Natsis in her impaired driving case is questioning the impartiality of an OPP collision investigator who wrote a report that found her at fault in the crash.

The crash on Highway 17 between two SUVs left one man dead. (Supplied photo)

In court on Thursday, Crown lawyers wanted to introduce collision investigator Shawn Kelly as an expert witness capable of deconstructing what happened on the night of March 31, 2011.

That night, Natsis's Ford Expedition struck a truck head-on on Highway 17, killing the driver of the truck, 50-year-old Bryan Casey of Ottawa.

Court adjourned Thursday before Ontario Court Justice Neil Kozloff could rule on whether to allow Kelly's testimony as an impartial expert.

Investigator had made up mind about blame, defence lawyer claims

Defence lawyer Michael Edelson questioned whether Kelly should be considered an impartial witness and he suggested the OPP investigator decided Natsis was to blame when he wrote his report.

"Have you ever heard of the expression, 'tunnel vision,' in the legal context?" Edelson asked Kelly at one point while the investigator was on the witness stand.

Kelly denied the insinuation his impartiality was compromised in writing the report, which found Natsis at fault in the crash.

Edelson also questioned Kelly about his communication with the investigating officer. He said, for an impartial observer, Kelly had "injected [himself] into areas of the investigation not relevant to the crash."

Judge yet to rule on breathalyzer evidence

Natsis was impaired at the time of the collision, according to the testimony of Crown witnesses. But Kozloff has yet to rule on the admissibility of the breathalyzer evidence.

Dr. Christy Natsis is charged with impaired driving causing death, dangerous driving causing death and exceeding the legal blood-alcohol limit. (CBC)

Kozloff must also rule on whether Natsis's Charter rights were breached during her arrest.

The court also heard the victim, Bryan Casey, had a blood alcohol level close to 1.5 times the legal limit.

On Wednesday, the court heard from an automotive engineer who said data from a control module in Natsis's vehicle showed she did not use the brake in the seconds leading up to the collision.

Natsis is charged with impaired driving causing death, dangerous driving causing death and exceeding the legal blood-alcohol limit. She has pleaded not guilty to the charges.