A Launceston Supreme Court jury took just more than two hours to find Mark Rodney Jones guilty of murder.
The 43-year-old West Launceston man faced an eight-day trial after pleading not guilty to murdering Bradley Breward on New Year's Day in 2017.
Jones had been looking for Mr Breward over the theft of his stolen Nissan Patrol in December 2016.
A bounty was put on Mr Breward's head, as well as a $5000 reward offered for the return of the stolen car.
Tina Robertson was in a relationship with Mr Breward's friend Cody Lee and gave up the victim's location the morning he was killed.
The court heard Ms Robertson was upset with Mr Breward after he insinuated she'd had sex with another man, so she left her boyfriend's Newnham unit and called Jones.
The killer and his employee Ricky Izard went to the unit to get information out of Mr Breward about the stolen Patrol.
But the victim did not disclose anything the stolen car, making Jones angry.
Mr Breward was punched, kicked, waterboarded and had a plastic bag wrapped over his head by Jones.
Before the plastic bag was held over Mr Breward's head for the second time, he told Jones he was dying.
But Jones didn't believe Mr Breward, placed the bag over the victim's head and counted to 40.
Mr Breward was blue when the bag was removed, so Jones, Izard and Mr Lee attempted to give him CPR.
When Mr Breward didn't regain consciousness his body was wrapped in a beanbag and tarpaulin, and put in the back of Jones' car.
Jones and Izard went to Mowbray Woolworths to buy Mr Lee cleaning products and food because Jones thought it "was the right thing to do".
- DAY 4 AM: Jury visits unit where Bradley Breward allegedly killed
- DAY 4 PM: Mark Jones and two other men tried to give Bradley Breward CPR
- DAY 5 AM: Bradley Breward's injuries detailed by forensic pathologist
- DAY 5 PM: Mark Jones didn't leave unit in fear of looking like a 'goose'
- DAY 6: Prosecutor says jury can be satisfied Mark Jones guilty of murder
- DAY 7: Alternative verdict of manslaughter offered to jury
Desperate to get rid of Mr Breward's body and avoid being charged with murder, Jones drove around Lilydale for three hours looking for a mineshaft to dump the body.
After he failed to find it, Jones and Izard went to Launceston Kmart to buy a raft and stopped at a Latrobe house to pick up 35-kilograms of weight plates that the former bodybuilder had lent to a friend.
Electrical cord and rope were used to wrap the plates like a harness around Mr Breward's body before using the raft to move his body into the water at Lake Eugenana.
Also known as Melrose Quarry, the lake was somewhere Jones had spent a lot of time as a child growing up at Forth, so he knew the area well.
Jones and Izard drove to a friend's house at George Town to burn everything that could potentially have DNA on it.
Izard pleaded guilty on June 11 to the manslaughter of Mr Breward.
The 28-year-old South Launceston man will appear in the Supreme Court for sentencing on July 1.