"I don't even know how to begin to apologise for this," he said, looking toward Richard Beehag, his victim's brother.

"I'll keep trying to make up for it but I know it's a lifelong thing. I'm terribly sorry."

Mr Beehag's sister Amanda Beehag, 53, was driving home from work on May 4 last year when a police car driven by Chancellor flew into a Kaleen intersection.

He had been driving more than 100km/h in a 60km/h zone. The car's lights were on but not its sirens when he entered the intersection of Baldwin Drive and Maribyrnong Avenue. He braked, but couldn't avoid Ms Beehag's Hyundai Getz.

He T-boned her car and Ms Beehag suffered a brain injury, fractured vertebrae and ribs, and two collapsed lungs. She died after her life support was turned off on June 1.

A police radio recording played to court revealed Chancellor was responding to what was described as a high priority call out just before 8pm, of a male prowler wearing all black and holding a torch sneaking around a construction site in Bruce.

It was Mr Beehag who turned off his sister's life support after five weeks in an induced coma. But he told the court his family held no ill-feeling towards the officer. He acknowledged the crash was like so many others, but that this one was different because it had been a public servant and police officer behind the offending wheel, a man who had received specialised training and was entrusted with providing safety and security to the public.

On that, Mr Beehag hoped, lessons might be learned from his sister's death and changes made to police procedure or process. "Please do not let my sister's death be in vain," he told the court.

Chancellor, 38, pleaded guilty in March on the day his trial was due to begin to a charge of negligent driving causing death. He appeared in the ACT Supreme Court on Tuesday for a sentence hearing.

Chancellor told the court he had been employed as a police officer from August 2006 to March 2019. He was posted to Melbourne and travelled to the Ukraine twice to work on the investigation into the MH17 airplane crash. He was the first to Ms Beehag's aid, giving her several breaths of air and waiting with her until the ambulance arrived.

Chancellor also gave a damning assessment of the Belconnen police station's fleet of cars. On the night of the crash, Chancellor had returned one of the sergeants' Holden Commodores when he realised the transmission was faulty while out on a job. He was driving in the second car when the crash happened.

It later emerged the second Commodore had three bald tyres - that Chancellor said would be booked if on a civilian car - and deficient brakes. He said the cars were not looked after because of a lack of staff and that he had raised the quality and condition of the cars with his superiors. He said he wouldn't have driven the car under urgent driving conditions if he had known.

It also emerged during the hearing that Chancellor had a driving record that included seven speeding infringements in the three years from 2014. But Chancellor denied he was a person with a tendency to speed.

He said he was aware of the impact of court processes on victims and despite pleading not guilty to the charges to begin and almost starting a Supreme Court trial, said he was always willing to plead guilty. He had reviewed the urgent driving guidelines when he returned to the ACT, including the obligation to slow down and only enter intersections when safe to do so.

He told the court he had resigned from the police force. "I didn't think the public would have faith in my coming back." With a complaint still against him in relation to the crash, he was told the door was shut to ever returning.

Defence barrister Steven Whybrow said Chancellor accepted it was his driving, his decisions and his error of judgment that led to Ms Beehag's death. But he said the condition of the car was not irrelevant. "A police officer should never have been put in that position, of driving a car in that condition under urgent driving conditions."

Even a small improvement in braking speed would have changed the nature of the crash from a fatal T-bone, to striking the back of Ms Beehag's car, the barrister said.

He said that in this case a non-conviction order, or no more than a good behaviour order, was called for in sentencing.

But prosecutor Rebecca Christensen said Chancellor's negligence was of a high level and multi-faceted.

He had been speeding, failed to use his siren, and had entered an intersection against a red light, in circumstances where he had been engaged with finding an address on his GPS. His conduct was well below the police's urgent driving guidelines for entering intersections, Ms Christensen said.

The substantial deviation from standards had the potential to erode community confidence in the police force, she said.

She noted his late plea and that Tuesday was the first time Chancellor had offered an apology.

Justice David Mossop will sentence Chancellor on Thursday.