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Jury warned during cop's pursuit death retrial

The jury in a retrial of a NSW police officer accused of causing a motorcyclist's death while on duty has been warned to focus only on the evidence heard in court.

Matthew James Kelly has pleaded not guilty to manslaughter and is also facing an alternate charge of dangerous driving occasioning death.

Kelly was driving a NSW Police Force Kia Sorrento in the early hours of April 16, 2020 when he pursued Jack Roberts, who was riding an unregistered, unregistrable Honda trail bike up the Pacific Motorway at Blue Haven on the Central Coast, before the two vehicles collided.

Mr Roberts died at the scene.

How the 28-year-old died will be in contention.

A forensic pathologist had ruled the cause of death as traumatic asphyxia, crown prosecutor Craig Everson SC told the jury in the NSW District Court on Tuesday.

"The heavy weight of the police vehicle severely interfered with his ability to breathe normally," Mr Everson said.

Kelly's lawyer James Glissan KC said there would be competing theories about the cause of death of Mr Roberts, who the jury would hear was on drugs at the time.

Mr Roberts "was endeavouring for some time at least to evade police", Mr Glissan said.

However, he had "effectively disappeared from view" after turning onto Blue Haven Way, before coming across the front of the Kia at an angle, Mr Glissan told the jury.

He said it was up to the jury to decide whether Mr Roberts was in fact "trapped" under the car.

"In the sense that there is any pressure on him, or if he was trapped by an object and couldn't be removed," Mr Glissan said.

The jury could expect evidence about Kelly's conduct of the pursuit not being consistent with police policies, but non-compliance with an employer's policies is not necessarily unlawful, he said.

Judge Penelope Hock stressed to the jurors to focus on the evidence they hear in court and not appoint themselves investigators.

Kelly previously faced a trial in which the jury was discharged during deliberations when it emerged a juror had conducted their own experiments.

"For the trial, which took a number of weeks, to get to that stage where the jury was actually deliberating, caused not only massive inconvenience and stress to the accused and all the witnesses who now have to be recalled ... the jury had to be discharged due to the possibility of a miscarriage of justice," Judge Hock warned the new jurors.

Fifteen people have been empanelled for the jury, with the verdict to be decided by 12 following a ballot once the opposing cases are presented.

The trial continues on Wednesday.