Mining engineer Tony Campbell had just fulfilled a lifelong ambition to complete the Sydney to Hobart Yacht Race in 2019, and his wife Bernice was turning 40.

They decided to travel around Tasmania together in January 2020, away from their three children aged 13, 10 and seven back in their hometown of Singleton, NSW. They were already planning to retire in the Apple Isle.

READ MORE Senator Penny Wong lands in Tasmania to announce $8 million Tamar Estuary plan

"It was a glorious week of freedom and spontaneity ... exploring, walking in nature, beautiful dinners, uninterrupted conversations," Mrs Campbell told the Supreme Court in Hobart on Friday.

"In an instant, it was all gone."

On the evening of January 6, just before 8.30pm, the couple had finished an Indian meal in Launceston and were walking along Paterson Street in the CBD when then-police officer Aaron Tasman Bonner - an acting sergeant that night - pulled out of a car park nearby.

Bonner, 41, was sitting in a marked police car at the Birchall's car park when another unit requested assistance in handling a mental health incident in Launceston's southern suburbs.

It was not considered an urgent call, the court heard.

Bonner exited the car park onto Paterson Street and turned on his lights and siren. Just over 100 metres up the road at the intersection of St John Street, the light was red and another couple was crossing.

The court heard the couple saw a police car accelerating towards the intersection and they ran out of the way. In the space of 115 metres, Bonner had accelerated to 89 kilometres per hour. The court heard the accelerator was pressed down to 99 per cent when he went through the red light.

At the same time, a family-of-four were driving along St John Street towards a green light. Bushes and trees meant the driver had no idea that Bonner was speeding towards the intersection.

Bonner's police car was t-boned and became airborne while spinning, then rolled as it hit a parking meter.

It struck both Tony and Bernice Campbell.

In that split second, neither had a chance to get out of the way.

READ MORE: NBL: Peter Gutwein praises Tasmania JackJumpers, puts AFL on notice

Twelve pedestrians saw the collision and many rushed to their aid, while a further 14 people were witnesses in nearby vehicles. Bonner, uninjured, also rendered assistance before other police units arrived.

Mr Campbell was taken to the Launceston General Hospital, but was pronounced dead soon after. Mrs Campbell suffered catastrophic injuries, undergoing four surgeries at The Alfred Hospital in Melbourne before she was flown to Newcastle in an induced coma, discharged over a month later.

The collision left a family broken forever.

This week, the wider Campbell family travelled down to Hobart as the court proceedings reached their eventual conclusion.

Bonner had pleaded guilty to causing death by dangerous driving, and grievous bodily harm by dangerous driving. A sentencing hearing on Friday gave the family the chance to detail their ongoing grief.

Bernice Campbell told the court how she had lost her soulmate and best friend - that they had been together since year 12 at high school and got married aged 25.

"Tony and I were together for more than half our lives," she said. "He was the most loving dad.

"We built a life and a future. Hopes, dreams, memories and plans, so many plans."

READ MORE: National Institute for Forest Products Innovation will be headquartered at Newnham

Along with the toll of losing her husband, Mrs Campbell also faced a long physical recovery. She spent four months in a wheelchair and had to learn to walk again, but is still severely limited.

"I'm now back in a body that is broken," she said.

"[I am] now where I'm walking ... not fast, not pretty and it's far from comfortable."

As Bonner sat in the dock, Mrs Campbell said she had started to feel forgiveness.

"I do feel for you, for the burden of guilt you must carry with you," she said.

Tony's father detailed how he had lost his best friend, while his mother and sister spoke of their ongoing sadness for the whole family.

Despite police having an exemption to drive through red lights when appropriate, they must also exercise a duty of care to the public, the court heard.

Crown Prosecutor Emily Stone said Bonner had breached this.

"It is asserted that the accused placed a significant number of people at risk by his dangerous driving," she told the court.

She highlighted evidence showing the accelerator was "essentially foot to the floor" as Bonner approached the red light.

Ms Stone claimed that Bonner's actions amount to a "breach of trust" and that it "erodes community trust in police officers", as mentioned by several Campbell family members in their statements.

Defence counsel Patrick O'Halloran highlighted a psychiatric report which showed Bonner had "intense survivor guilt", and may have already been "highly traumatised" before the crash due to his previous police work responding to intense situations.

He has since been diagnosed with post-traumatic stress disorder as a result of the crash.

Mr O'Halloran said Bonner had no prior police conduct breaches and had a "good record" as an officer, since graduating into the force in 2008.

His father had been seriously injured as a police officer while responding to a mental health callout, Mr O'Halloran said, which may have explained his desire to get to the callout as soon as possible.

READ MORE: Tasmanian business leader Gerald Loughran remembered

Bonner had told attending police that he had "cleared the intersection" before the collision, but has since admitted this was incorrect.

Bonner resigned from Tasmania Police this week after he previously pleaded guilty.

Justice Robert Pearce said the offending was "a very serious failure to take reasonable care" and a "terrible error of judgement.

"This is a tragic case from every perspective," he said.

"No sentence of whatever length can make up for, or undo, the harm that was done."

Bonner was jailed for three years with a non-parole period of one year and six months.

Our journalists work hard to provide local, up-to-date news to the community. This is how you can continue to access our trusted content: