A jury found Cain Moss guilty of first degree reckless homicide and hiding a corpse.
Moss delivered the drugs that killed 40-year-old Anthony Ducharme and dumped his body in a north side park on August 4, 2011.
Jurors began deliberation around 11:15 a.m. and reached their verdict at about 1:15 p.m. They heard testimony from Monday through Thursday in La Crosse County Court.
Prosecutors said Moss and his girlfriend, Christina Lorenz, bought a Fentanyl patch, a narcotic painkiller, and gave it to Ducharme at Moss's father's home. The prosecution says Ducharme overdosed on that drug after taking just one hit.
Cain Moss, his father, Robert Moss, and their friend Patrick Valiquette are accused of then dumping Ducharme's body in Red Cloud Park.
Robert Moss pleaded no contest to party to the crime of hiding a corpse. He was sentenced to a year in prison followed by two years' extended supervision.
Lorenz pleaded guilty to a reduced charge of second-degree reckless homicide and was sentenced to four years in prison. A party to the crime of hiding a corpse charge against Lorenz was dismissed.