A fatal head-on crash on Highway 17 happened in the victim's lane, an Ontario Provincial Police officer told an Ottawa courtroom today.

Const. David Dunfield was the first officer to arrive at the March 2011 crash that killed 50-year-old Brian Casey of Ottawa.

Pembroke dentist Dr. Christy Natsis is charged with impaired driving causing death, dangerous driving causing death and exceeding the legal blood-alcohol limit in the crash.

Natsis has pleaded not guilty to all three charges.

Dunfield testified that based on what he saw when he arrived at the crash scene, the collision happened in the eastbound lane, which was the lane Casey used while heading home to Ottawa.

"I saw the accident happened in the eastbound lane. The main debris field was in the eastbound lane," Dunfield told the court.

According to earlier testimony from passersby, Natsis told retired teacher Dan Quinn and his friends that the white SUV driven by Casey drifted into her lane and struck her black SUV.

Dunfield's testimony disputed that, but defence lawyer Michael Edelson pointed out many vehicles had driven through the debris before he arrived.

Charter defence coming, lawyer says

Edelson also brought forward a new defence strategy Thursday, saying he will challenge how and when Natsis was arrested and when she was granted access to a lawyer.

The OPP constable testified he believed Natsis was "intoxicated," saying she "stumbled severely" and "almost fell over."

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

During testimony Wednesday, Ottawa paramedic Brock Smith said Natsis could barely walk and had to be supported on the 18-metre walk to the ambulance. He also said she smelled of alcohol.

The passerby, Quinn, also told the court Tuesday Natsis was "unsteady" and it looked like she was "going to lose her balance." But when pushed by the defence lawyer for the accused, Michael Edelson, Quinn admitted anyone would look unsteady after a serious crash.

Edelson pushed Dunfield on whether the victim also smelled of alcohol or if he was aware Casey had alcohol in his vehicle.

Dunfield said no, as did two earlier witnesses.

The paramedic also told the court Wednesday the crash was the worst he had ever seen.