Connor Harley Latty, 20, died when the driver-less vehicle rolled down a hill and hit him as he walked along Police St.
The Dunedin District Court this week heard Robert Gerwyn Hutton, 66, of Christchurch, was having mechanical issues with the truck and trailer unit on March 17 last year and got out to investigate, but failed to engage the handbrake, causing a trail of destruction.
The victim’s father, Dean Latty, said he had been haunted by the tragedy.
"I’m not sleeping and I have dreams about how my son died. I can’t help but think about how his life came to an end, the thought of the moments before he died. Did he know what was happening?" he wrote in a statement.
"[It] causes me unbearable pain."
The victim’s mother, Donna Cooper, described her son as "a loving, caring, wonderful young man".
Her agony was only compounded by the horrific wounds he suffered.
"Not being able to see his face, kiss him goodbye because of his injuries ... the only part of the body intact was his left hand," Ms Cooper said.
"The loss of my son has torn everything inside me apart."
The defendant had parked in Carroll St on the morning in question, facing downhill, and began to unload damaged vehicles at an autoparts company, but his progress was hampered by problems with the trailer.
When Hutton tried to drive away there was a shuddering and he realised the brake for the rear trailer was still engaged.
He disembarked to manually release it but left the handbrake off and the tragic chain of events was set in motion.
The truck careened across Princes St, into Police St where it hit a parked car, then collided with Forno’s Auctioneers, before striking Mr Latty.
The momentum took the vehicle across Crawford St where it smashed into four vehicles and finally came to a stop.
There was some conjecture over whether an alarm — which would sound if the driver opened the door without applying the handbrake — was working, but Crown prosecutor Richard Smith said ultimately it mattered little.
The fact Hutton was having issues with the truck and forgot to pull the handbrake was a severe oversight, he said.
Counsel Kelly Beazley said her client was traumatised by the incident and had been diagnosed with PTSD.
His fixation on the alarm was out of a desire to understand how he could have made such a catastrophic error, she said.
The court heard Hutton had no previous convictions and Ms Beazley stressed his "good character" having volunteered at the Christchurch Children’s Christmas Parade Trust for more than 20 years.
Judge Jim Large accepted the defendant had not meant to cause any harm that day, but there was no escaping the fact he was solely responsible for the death of a young man.
The statements of Mr Latty’s parents were some of the most "harrowing" he had ever read, the judge said.
"I could not conceive how difficult it could be for a parent to have lost a child in such circumstances," he said.
Hutton was sentenced to nine months’ home detention and banned from driving for 18 months.
He was ordered to pay reparation of $3000, a sum Mr Latty’s parents decided would go towards the medical studies of their son’s best friend.
