The image of Bruce Saunders' legs in a woodchipper kept Gregory Lee Roser awake at night, a court has heard.
Roser, 63, told police he "felt responsible" after Mr Saunders died while working on a property north of Brisbane in November 2017.
The Crown alleges Roser's girlfriend Sharon Graham asked him and another lover Peter Koenig to kill her ex-partner Mr Saunders and make it look like an accident in a bid to claim his $750,000 life insurance.
Police footage has been shown to a Brisbane Supreme Court jury of Mr Saunders' legs sticking out of the woodchipper at the Goomboorian property near Gympie after clearing trees with Roser and Koenig.
In video of a January 2018 police interview shown on Tuesday, Roser tells officers that he could not get the image out of his head after the "accident".
"All I could see, I see them all the time, are just these legs sticking out of the machine - it's coming back to me all the time," he said.
"I have had a lot of bad nights because of it. I keep seeing him in the back of that bloody machine.
"I wake up in the middle of the night and I can't get back to sleep."
Roser tells Detective Sergeant Christopher Duhig that he tried to save Mr Saunders when he saw his friend in the machine.
Roser said he grabbed Mr Saunders by the ankles but the body wouldn't budge.
"I actually thought he had only just gone in ... so I grabbed him to try and pull him and he wouldn't come," he said.
"It was like he was locked in there."
After screaming for help, Koenig shut down the machine with Roser still holding onto Mr Saunders' ankles, the court heard.
Asked by Det Sgt Duhig whether he thought Mr Saunders was dead at the time, Roser says: "No, I don't think so, that's why we rang the ambulance ... it was really horrible".
Roser said he had experience with chippers and became physically ill afterwards because he felt responsible.
"I was really upset because this has never happened to me ever," he told police.
"I got a fair bit to do with these machines, I felt responsible."
Det Sgt Duhig asked: "In what way?"
"Just that he (Mr Saunders) wouldn't listen," Roser replied.
Roser told police that Mr Saunders had been reckless around the machine and was at one stage banned from using it.
He said Mr Saunders was constantly on his mobile phone around the machine and was once seen using his feet to feed branches into it.
Roser said Mr Saunders had also earlier been hit in the head by a falling branch, leaving him dazed and bleeding but he refused medical treatment.
"I said 'mate you are not doing it properly, you are going to get hurt ... you don't realise that this machine is so dangerous'," he said.
"He (Mr Saunders) was like 'I am right, I know what I am doing'. He was really pig headed."
An ambulance was not called until Roser and Koenig walked up to the property's house and told the owner about Mr Saunders.
Roser has pleaded not guilty to murder.
The trial before Justice Martin Burns continues.