An ex-amateur bodybuilder who tracked down and killed a 22-year-old man during a torture session has been found guilty of murder.

Key points: The victim's body was found by police divers at the bottom of a lake

The victim's body was found by police divers at the bottom of a lake A girlfriend of one of the victim's friends told the killer where the victim could be found in exchange for $1,000

A girlfriend of one of the victim's friends told the killer where the victim could be found in exchange for $1,000 The murderer's lawyer argued the death, caused by suffocation by a plastic bag, was a "tragic accident"

The court heard 43-year-old Mark Rodney Jones killed 22-year-old Launceston man Bradley Wade Breward on New Year's Day in 2017 because the young man had supposedly stolen his car.

Jones, a former bodybuilder, had pleaded not guilty to the murder charge, but a jury took two hours to unanimously find him guilty at Launceston Supreme Court on Wednesday morning.

During the trial the court heard Jones and his employee Ricky John Izard, 28, then tried to cover up the murder by dumping Mr Breward's body in Lake Eugenana in the state's north west with weights attached to it.

The pair also burned Mr Breward's clothes and the life raft they used to dump his body in a 44-gallon drum in George Town the night of the murder.

Izard has previously pleaded guilty to manslaughter, aggravated burglary and perverting the course of justice.

Throughout the eight-day trial, the court heard Jones' Nissan Patrol was stolen from the side of the road in Prospect Vale in early December 2016.

Jones then became "obsessed" with finding his car and offered a $5,000 reward for its return.

After hearing from numerous people that Mr Breward had stolen it, Jones tried to track the young man down, the court heard.

'On the trail' of victim for weeks

The court heard Jones messaged his friend Timothy Haab just days before the murder and told him: "I'm on the trail of Brad Breward … c***'s gonna pay, he's gonna die and be brought back to life many times over".

Brad Breward, who died after being tortured by Mark Rodney Jones over allegedly stealing a car. ( Instagram: Brad Breward )

The court heard the girlfriend of a friend of the victim told Jones where Mr Breward was the morning of the murder, in exchange for $1,000.

Jones and Izard entered the unit Mr Breward was staying at the morning of January 1, 2017 armed with a screwdriver and tape, the court was told.

The pair found Mr Breward asleep on a couch, woke him, tied up his hands with tape and then Jones started punching and kicking him.

Jones then tortured Mr Breward, by covering his face with a towel and then pouring water over it — a technique known as waterboarding — and later suffocating him with a plastic shopping bag to get information about his stolen car.

"Mr Breward didn't give him any information," Crown prosecutor Daryl Coates told the court in his opening address.

"On the last occasion [of placing a bag over his head] … Mr Breward suffocated and died.

"The accused, by assaulting and then placing a plastic bag over the deceased's head, ought to have known that could have caused Mr Breward's death."

Divers found Mr Breward's body in Lake Eugenana near Devonport. ( Supplied: Discover Tasmania )

'An accident', defence claimed

Jones' defence lawyer Greg Richardson argued throughout the trial that the death was "not murder" and was instead "a tragic accident".

Mr Richardson told jurors in his closing address to consider Jones' intention for wanting to find Mr Breward.

"Mr Jones's motive, his whole purpose, was to get his car back," Mr Richardson said.

"Stop and ask yourself, why on earth would you choose to, or why on earth would you intend to kill the one person on earth who knew where your vehicle was?

"This was a tragedy for the young man who died. This was a tragedy for Mark Jones and his family who will be scarred for the rest of their lives … it was an accident.

"It was someone who did something out of desperation, it was not murder."

Sentencing submissions will be heard next week.

Izard will next appear in court on July 1.