Paul Williams: 'How Quirke planned perfect murder - but still got caught'
Patrick Quirke became a "person of interest" - official police-speak for suspect - within days of Bobby Ryan's disappearance, because he had a motive to murder.
The popular part-time DJ was in a relationship with widow Mary Lowry, who was Quirke's former secret lover. Quirke is married to her late husband Martin Lowry's sister Imelda.
That morning, Bobby Ryan left Ms Lowry's home at around 6.30am to go to work in a nearby quarry, but he never turned up and she later reported him missing to gardaí, who launched an investigation.
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Investigators first had to assess the possible reasons for the disappearance in a process of elimination with three scenarios to consider: Mr Ryan had inexplicably decided to go somewhere without telling anyone; he had taken his own life, or he had been the victim of foul play.
But the testimony of those closest to the missing man quickly ruled out the likelihood of his leaving or taking his own life.
As pointed out by prosecutor Michael Bowman SC in his summing up of the State's case, Mr Ryan was a man who loved life, his job, music and dancing and was universally loved and liked.
He had been in a meaningful relationship with Ms Lowry for almost a year and he dearly loved his children, Robert Jnr and Michelle.
"Who would want to kill Mr Ryan and strip him of his possessions, his clothes, his dignity, and leave his body to decompose for 22 months in a sealed chamber on a farm in Tipperary?" Mr Bowman asked the jury.
The answer was Patrick Quirke - who emerged as a suspect after gardaí had ruled out other possible scenarios.
- Read more: Maeve Sheehan: 'Two bright red spots on Patrick Quirke's cheeks the only giveaway of the turmoil beneath that implacable surface'
Quirke's motive for murder began to materialise from the statements of Ms Lowry and others. A relative of Mr Ryan told gardaí that Mr Ryan said that Quirke had threatened his life if he didn't back off. However, this information was not presented as evidence before the jury on the grounds that it was hearsay.
But a clear motive was emerging from the testimony of witnesses: the killer, who was not known as a violent person, had been driven by jealousy and the warped hope that with his love rival out of the way, he could rekindle his secret affair with Ms Lowry.
And while gardaí had strong, reasonable suspicions, there was no evidence on which to mount a murder charge.
An extensive land search by gardaí failed to locate a body, and when detectives interviewed Quirke, he gave nothing away.
In the absence of a body, gardaí could not prove that a murder had even taken place, so the investigation file remained open as a missing person case.
But then, almost two years later, on April 30, 2013, there was an unexpected breakthrough when the prime suspect reported "finding" human remains in an overgrown slurry pit on Mary Lowry's farm, which Quirke had been renting.
Having confirmed that the remains were those of Bobby Ryan, gardaí began to develop a theory as to how the murder had taken place.
Quirke had possibly been lying in wait for his love rival as part of a pre-ordained plan, or had attacked Mr Ryan in a fit of rage as he left Ms Lowry's home on the morning he vanished and then dumped his naked remains into the covered disused slurry pit.
The pit had been so well concealed under a carpet of muck and grass that gardaí missed it during the initial searches of the property.
It was no coincidence either that the timing of the discovery by Quirke overlapped with the imminent termination of his lease of Mary Lowry's lands. This dramatically increased the risk that the remains would be discovered when work was carried out on the area of the overgrown slurry pit.
By finding the remains himself, Quirke reckoned it would serve to divert blame from him and on to Ms Lowry.
And so gardaí began the painstaking process of building a wall of mostly circumstantial evidence in a case that the prosecution conceded was "forensically barren".
In the initial stage of the murder investigation, detectives suspected that Quirke was on the brink of a nervous breakdown and might confess his role in the crime.
They had been told that he was plagued with guilt and remorse for the murder of Mr Ryan, believing the subsequent tragic death of his son was the result of bad karma.
However, when gardaí did arrest the prime suspect, he robustly denied having any part in the crime and attempted to shift the suspicion on to his former lover.
Among the evidence gathered by gardaí that exposed Quirke as a liar was that of a forensic entomologist, an expert in insects, who established that the slurry tank containing the body had been opened at up to two weeks before Quirke claimed he made the discovery.
Like so many killers before him, Quirke unconsciously left a trail of circumstantial evidence on his computer, including searches for "body decomposition timeline".
When detectives questioned Quirke about this, he told them his son had died and "that's all I'm saying".
But a forensic search of his computer showed that the killer had carried out similar online searches before his son's death, which took place in August 2012, thus exposing another lie.
Further evidence revealed searches for wife killer Joe O'Reilly and reports of how he was caught.
Quirke, like O'Reilly, probably assured himself that he had covered his tracks and would not get caught - he had pulled off the perfect murder.
Now Quirke has plenty of time to share notes with O'Reilly and work out where he went wrong.