A veteran crash reconstructionist for the Ontario Provincial Police admitted he missed mistakes made by a fellow officer in a report into the 2011 crash on Highway 17 that killed Bryan Casey of Ottawa.

Pembroke dentist Christy Natsis was charged with impaired driving causing death, dangerous driving causing death and exceeding the legal blood-alcohol limit after her SUV crashed head-on with Casey's pickup truck in March of 2011.

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Christy Natsis was charged in the fatal crash, which happened more than three years ago along Highway 17 near Arnprior, Ont.

Speaking at her trial on Monday in an Ottawa courtroom, OPP Const. Robert Kern told the court he peer reviewed the crash report of fellow crash investigator Const. Shawn Kelly.

In the report Kelly concluded the crash was Natsis' fault but admitted he made several mistakes in his investigation.

Kern said on Monday he didn't catch the mistakes when he reviewed Kelly's findings.

He added he only picked up on his oversights when media reports from the trail emerged. 

'It was an error on my part'

Kern said Kelly made a mistake on the direction Natsis' vehicle was facing after the crash. 

He added he also misrepresented skid marks and failed to identify other tire marks on the shoulder likely made by emergency vehicles.

Kern said in re-examining Kelly's report "certain things were overlooked on my part."

"I take full responsibility — it was an error on my part," Kern told the court.

Kern says the process of peer reviewing collision investigators was already being revamped when the 2011 crash occurred. 

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The family of Bryan Casey, left, is awaiting the end of the criminal trial before it can pursue a civil case against Natsis. (Submitted photo)

He said there is now much more oversight now, with more investigators reviewing reports to catch any possible mistakes.

Kern, the OPP's lead collision reconstructionist for the Eastern Ontario region, is expected to be the last Crown witness in the trial.

Natsis's trial began in November 2012 but has been delayed several times for the judge to rule on the admissibility of evidence.

There have also been several scheduling conflicts with the lawyers, who say it’s likely one of the longest impaired driving trials in Canada. The trial only sat for four weeks this past fall.

When the trial adjourned in November, defence lawyers had finished their cross-examination of Sgt. Mark Wright, the OPP's head of the technical collision investigations and reconstruction program.