Bobby Ryan's death was "callous, calculated, controlled murder" and the only verdict available is to find Patrick Quirke guilty of murder, lawyers for the State have told the Central Criminal Court.
The defence says the prosecution evidence is thin and warned the jury of the dangers of accepting the evidence of Mary Lowry.
Mr Quirke (50), of Breanshamore, Co Tipperary, has pleaded not guilty to the murder of Mr Ryan, a father-of-two and part-time DJ known as 'Mr Moonlight'.
Mr Ryan went missing on June 3, 2011, after leaving his girlfriend Ms Lowry's home at about 6.30am. His body was found in an underground run-off tank on the farm owned by Ms Lowry and leased by the accused at Fawnagowan, Tipperary, in April 2013.
The prosecution has claimed Mr Quirke murdered Mr Ryan so he could rekindle an affair with Ms Lowry (52).
Finishing his closing speech to the jury of six men and six women, Michael Bowman SC, for the prosecution, said for a guilty verdict he must rule out any rational theory that would be consistent with Mr Quirke's innocence.
Ruling out suicide, he said Mr Ryan met with a "violent and brutal death".
He ruled out accident, saying accident does not have the "hallmarks of concealment of a criminal act". This body, he said, had been stripped naked for forensic reasons and his death was "callous, calculated, controlled murder".
The prosecution cannot identify a specific weapon or time of death but, he said, it is clear that he died after leaving Ms Lowry's home at 6.30am on June 3, 2011.
His body was found 22 months later, "not 60 yards from where he got out of bed that morning".
Taking the jury through the "strands" of evidence, he said each one would amount to nothing more than suspicion or something uncannily coincidental but it was the combined effect that was important.
The evidence, he said, clearly communicates motive.
The recovery of the body, he added, is "anything but fortuitous but planned and designed."
"Bobby Ryan was murdered by somebody possessed of information and knowledge possessed only by Patrick Quirke," he added.
"Patrick Quirke is guilty of the murder of Bobby Ryan on June 3, 2011. There is no other rational hypothesis consistent with innocence.
"The evidence has been laid painstakingly before you over the last 13 weeks. When you weave those strands together it is of sufficient strength to bear the burden and weight placed upon it.
"There is no room left to doubt and the only verdict available to you is one of guilty of murder."
Defence counsel Bernard Condon SC told the jury that the prosecution evidence was thin and that Mr Bowman had sought to do its job for it.
He warned the jurors of the dangers of accepting beyond reasonable doubt the evidence of Ms Lowry.
He said the prosecution was based on theory and circumstantial evidence and there was no hard evidence.
He asked them to apply their "greatest skill: scepticism".
He said the trial is "forensically barren" on what happened to the "unfortunate Bobby Ryan. His last movements, interactions, events, we know nothing about".
He said many of the allegations made by Ms Lowry, "wouldn't last five minutes in a court where that allegation was being made on its own".
At the heart of much of what went on between her and Mr Quirke, he said, is a broken relationship.
He described their relationship as "dysfunctional". They had an affair, he said, but "this is not a court of morality".
Mr Condon will continue his closing speech to the jury on Monday in front of Ms Justice Eileen Creedon.