A Brisbane man charged with killing his uncle, who vanished 20 years ago, has been found guilty of murder and sentenced to life in prison.

A Supreme Court jury in Brisbane deliberated for more than a day and a half before finding Robert James Wagner guilty of murdering his uncle Gerhard Wagner in 1999.

The 61-year-old was last seen leaving his friend’s business in Hemmant on his motorbike on the afternoon of January 7, 1999.

His body has never been found.

Prosecutor Phil McCarthy said Robert Wagner, now 57, had committed a “heinous crime against a person who regarded him as a son”.

“His death had left an inevitable hole in his family unit,” he said.

Justice Peter Applegarth said greed was the motivation behind the “cold-blooded” crime.

“[Your uncle] was generous emotionally and financially to his family,” he said.

“His reward was to be bludgeoned by [you]”.

Justice Applegarth said Robert Wagner remained free in the community until his arrest in 2014 after a renewed police investigation.

“[Gerhard] could have had a fulfilling, happy retirement that he’d worked so hard for,” Justice Applegarth said.

“The victims in this case are many.

“This family has had to suffer … with twists and turns in this case.”

The court had previously heard that Gerhard Wagner’s death was allegedly financially motivated because he had significant assets.

Robert Wagner had pleaded not guilty to the murder.

-ABC