BACKGROUND:Fundamental questions about how the victim died and where she died remain unanswered, writes RONAN McGREEVY.
MEG WALSH died an horrendous death. The blows that killed her had broken her skull into pieces, and some of those fragments were found in her brain.
It had been like "hitting a boiled egg", State Pathologist Dr Marie Cassidy told the jury.
There was evidence of injuries to her head, shoulder and right arm as if she had been involved in a terrible struggle.
Meg Walsh disappeared on Sunday, October 1st, 2006.
The last independent sighting of her alive was noon that day when a neighbour, Nicky Farrell, observed her in an upstairs bedroom putting clothes away. The last activity from Meg's mobile phone was just before 2pm that day when she accessed her messaging service.
Mr O'Brien said she left home at about 8.30pm on Sunday evening and drove off. She was never seen again.
The alarm was raised by Noel Power, Ms Walsh's employer at Meadow Court Homes Ltd, on the following morning when Ms Walsh did not turn up for work.
Despite an extensive Garda investigation and a lengthy trial, what happened to Meg Walsh on that Sunday has never been established.
Fundamental questions about how she died, where she died and when her body was dumped in the River Suir remain unanswered.
Instead, the prosecution depended on circumstantial evidence in their attempt to bring a case against her husband.
O'Brien first met Meg Walsh in Crete in 2000 when she was on holiday with her then husband Colman Keating.
The couple began an affair and she moved to Waterford in 2001. They married in October 2005. He too had been previously married.
There was evidence presented to the trial that their marriage was in trouble.
Ten days before she disappeared, Mr O'Brien assaulted his wife following an argument the couple had when they were out with his parents. Mr O'Brien admitted that "he lost it" with his wife on the night of September 20th.
Two days later Meg Walsh presented herself to her GP, Dr Bernadette O'Leary, with bruises and swelling to the backs of her hands and her right shoulder.
She also reported the assault to the Garda, but declined to press charges. Instead, she contacted her solicitor and bank manager about having the house transferred into her name.
Mr O'Brien told the jury that, following the assault, he had agreed to sign over the house to her "just to prove it would never happen again" and had agreed to loan her €11,000 to pay off credit card debts.
On the night before she disappeared, the couple spent the night drinking at the Woodlands Hotel near their home in the company of a mutual friend, Owen Walsh.
They invited Mr Walsh back to the house and she suggested that he stay the night. She showed him to the spare room, while Mr O'Brien went downstairs to turn off the lights. He then flew into a rage when he found the pair kissing in the spare bedroom.
In his first statement made to gardaí on October 2nd, he recalled: "I opened the door and saw Meg and Owen Walsh with their hands around each other, kissing. I said: What the f**k is going on? They stopped and Owen said: 'Sorry, sorry'". Mr Walsh later told the jury it was only a goodnight kiss.
Ms Walsh's disappearance prompted one of the biggest searches ever seen in the area. At one stage 2,000 people were involved. Her daughter Sasha Keating and brother James Walsh made a public appeal for information.
Her body eventually surfaced at Meagher Quay in Waterford city on October 15th.
John O'Brien was first arrested in December 2006 and was charged with her murder on June 22nd, 2007.
In the court, the prosecution relied on inconsistencies in his evidence and modern technological paraphernalia of CCTV footage, mobile phone movements and an electronic key fob.
He said he had gone to Tramore that Sunday to read the newspapers before returning home at around 5pm. However, CCTV footage picked up his car in Waterford City Centre that evening and he was spotted by the River Suir at 5.35pm.
When it was put to him in evidence, Mr O'Brien said he may have been mistaken about the time. When other allegations were put to him about inconsistencies in his evidence, he said that he had never thought her disappearance would lead to a murder investigation.
Ms Walsh's Mitsubishi Carisma was central to the prosecution case. Prosecution counsel Dominic McGinn said the car was "the real crime scene" as it was covered in her blood.
The car was found abandoned in the car park of the Uluru pub in Waterford city on October 4th.
CCTV footage was shown to the jury which purported to show Mr O'Brien parking the car at 10.03 pm on October 2nd, walking back to the Tesco Car Park where his own car was parked and then driving home, arriving there at 10.11pm, when he deactivated the alarm.
The prosecution also sought to argue that whoever killed Meg Walsh must have had a key fob to the Mitsubishi Carisma as it had been closed remotely and the only person who had such a key was Mr O'Brien.
However, the car may also have proved to be crucial in his defence. On the final day of evidence, a witness, Gregory Manberg, told the court that he had seen Ms Walsh's Carisma being driven around at 6.20pm on Tuesday, October 2nd, at the time when Mr O'Brien was giving a statement to gardaí about his wife's disappearance.
A unanimous verdict of not guilty was a serious rebuff to investigating gardaí.
And still the question remains: who killed Meg Walsh?