A New Zealand man accused of punching another driver who then fell into the path of an oncoming truck dry retched before asking a witness, "What have I done, what have I done?", a court has heard.
Tamate Henry Heke allegedly struck Shane Merrigan, 50, before the Brisbane man was fatally hit by a rubbish truck on the Gateway Motorway at Eight Mile Plains on December 1, 2015.
Mr Heke has pleaded not guilty to one count of manslaughter, as well as not guilty to an alternative charge of unlawful striking causing death.
Witness Jonathan Spillman told the Brisbane Supreme Court on Tuesday he had stopped to offer first aid after seeing a body lying on the road but when he got closer, realised it was too late.
While he didn't identify Mr Heke directly, Mr Spillman told the court he then turned his attention to a "Samoan, Islander type of person" nearby who had bloodshot eyes and looked like he was in shock.
"I asked him if he was OK," Mr Spillman said.
"At that stage he held out his two hands and said to me, 'what have I done, what have I done?'"
Earlier, fellow driver Eleanor Woodman said she saw a "Maori" man punch a Caucasian man in the face, then grab his head, pace up and down and dry retch after the man was hit by the truck.
"He was very distraught," Ms Woodman said.
Truck driver Peter Ratcliffe also described seeing a man of Pacific Islander appearance deal a heavy punch to another man and said he had put his "whole body" in it.
Another motorist, Jade Faulder, dabbed her eyes with a tissue as she recalled seeing a man fall back "kind of unconscious" onto the road after an encounter with a "Kiwi guy", followed by the moment of fatal impact.
Darren Whellum, a truck driver, didn't see an actual blow but said he witnessed a man fall back into the moving truck's path "almost like he lost his footing".
The jury has previously heard both men had been making their way home from work before pulling over to the left shoulder of the road and facing each other "for about 13 seconds".
The New Zealander is then accused of delivering a heavy blow to Mr Merrigan's head, causing him to fall into the path of the truck, which was travelling at 90km/h.
Photographs showing the truck's blood-splattered undercarriage were viewed by jurors on the first day of the trial.
They also saw graphic footage from a motorway camera showing the two cars pulling onto the road's shoulder, the men getting out, and the moment of impact.
But defence barrister Anthony Kimmins has said his client, a father of three, told police he didn't intend to get into a fight when he pulled his Holden Astra over that day.
The trial continues.