Robert James Wagner took advantage of his uncle's generosity and poor literacy by seeking to trick him out of his money, before bludgeoning him to death and dismembering his body, a Brisbane court has heard.

Key points: Robert Wagner positioned himself to benefit from his uncle's death before murdering him, the court heard

Robert Wagner positioned himself to benefit from his uncle's death before murdering him, the court heard Justice Applegarth says Gerhard Wagner was "brutally attacked" with a hammer

Justice Applegarth says Gerhard Wagner was "brutally attacked" with a hammer Credit card receipts for acid-protective clothing and masks helped police pinpoint the murderer

A Supreme Court jury in Brisbane deliberated for more than a day and a half before finding Robert 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.

In sentencing Wagner to life in prison, 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]".

Gerhard Wagner worked as a merchant seaman and was building a dream yacht boat to sail in his retirement when he vanished.

Justice Applegarth said Robert Wagner had positioned himself to benefit from his uncle's death.

"You took advantage of Gerhard Wagner's trust and his poor literacy by having him sign documents which directed all of the assets of a pending house sale to an account that belonged to you," Justice Applegarth said.

Robert James Wagner (R) tricked his uncle into signing over his property before killing him, the court heard. ( ABC News )

He said Robert Wagner persuaded his uncle "to sign a new one-page document which constituted a will … which would have left all of his estate under your control".

The court heard Gerhard Wagner, who was born in Germany, had also lent his nephew $300,000 to buy a property and allowed him to live rent-free in a unit.

Justice Applegarth said he was a hard-working, generous man who had planned to spend his retirement sailing his yacht.

Justice Applegarth said Robert Wagner had been waiting for his uncle when he arrived at his Ashgrove unit on the afternoon of January 7, 1999.

"He probably parked his bike in the garage and with the garage door down, you brutally attacked him [with a hammer]," he said.

"By chance, your cousin visited at 5:20pm that afternoon and you pretended not to be there and muffled the dying sounds of your uncle.

Over the following days, Robert Wagner dismembered his uncle's body and disposed of his remains in "rivers and mountains".

"You used acid for your evil deeds," Justice Applegarth said.

"You purchased acid-protective clothing and masks … and that was part of your eventual undoing. You used credit cards for your purchases."

He said Wagner, who had pleaded not guilty to the murder, stole his uncle's yacht, helped himself to its sale proceeds, and lied to police and others.

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."

'We always knew who it was'

Outside court, Gerhard Wagner's brothers said it had been a long quest for justice.

Peter Wagner said: "We've known from the start who it was, you know, 20 years ago, but just couldn't do anything about it."

Peter Wagner (left) and Paul Wagner (centre) said justice was a long time coming. ( AAP Image: Glenn Hunt )

Paul Wagner described the original murder investigation as "disappointing" but said the case came together when Detective Peter Roddick and his team began examining the murder as a cold case.

"As a family, we would like it to be known that Gerhard was a very much loved and respected member of our family," Paul Wagner said.

"Our hearts are broken for the loss of Gerhard ... he lost his life not because of he was a bad man, but because in fact it was the opposite, he was a good man, he was caring, he was generous, and he was trusting.

"We are particularly upset with the horrific way he was killed and his body was disposed of — you can't believe one of your family would do that.

"Thank you, Gerhard, for being a brother, brother-in-law, uncle and friend. We'll never forget you. Rest in peace."