"I am a broken man; physically, psychologically and emotionally," Garry Seary, the father of the 19-year-old victim, told the ACT Supreme Court on Tuesday.

"I am unable to work, unable to sleep and ... I have been to the brink of taking my own life on more than one occasion."

Facing court in a sentencing hearing was 29-year-old Gilmore man Peter Loeschnauer, who has pleaded guilty to charges of culpable driving causing death, a high-range drink driving charge, and driving with MDMA (ecstasy) in his system.

The court was told how the offender had been drinking firstly at Woden and then later at Braddon, where CCTV footage showed he had consumed up to a dozen alcoholic drinks before driving at high speed down the Monaro Highway on March 8. He later recorded a blood alcohol level of 0.186.

The speed camera at the Hindmarsh Drive overpass clocked his car at 141 km/h in a 100km/h zone, while police analysis of camera footage at Shepherd St, Hume, calculated the Honda driven by Loeschnauer was doing 157km/h in the 80km/h zone.

About 300 metres further on, the offender's car collided with the rear of the victim's Corolla and flipped it over the median guard rail and into a tree. Lachlan Seary was pronounced dead at the scene.

Seven people provided victim impact statements to the hearing before Acting Justice Verity McWilliam, including the victim's father, mother, sister, grandmother and aunt.

Relatives and friends choked back tears in the gallery as the statements were read, in a day which Acting Justice McWilliam later described as "distressing", and "very difficult for everyone".

Janice Seary, Lachlan's mother, said that "nothing could prepare us for the absolute devastation" that had been wrought on the extended family and the victim's huge network of friends.

She said the grief was "like a kick in the guts which takes my breath away".

She said that every time she saw a dark blue Corolla, such as her son drove, she was "paralysed with grief" and found it hugely difficult to maintain her composure.

"So many others are depending on us [her and her husband] for solace and support; it's exhausting," she said.

Lachlan was buried on March 17 last year, on what would have been his 20th birthday, in a plot beside his grandfather.

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The offender took the stand and under questioning from his barrister Jack Pappas, expressing his remorse for his actions.

He instructed Mr Pappas not to apply for bail, saying "I've got to pay for what I've done". He understood that he almost certainly faced imprisonment and was "terrified" about that prospect.

Acting Justice McWilliam revoked the offender's bail and adjourned the matter for sentencing on February 25.

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