Colm Murphy was originally sentenced to 14 years in jail
The only man jailed in connection with the 1998 Omagh bombing has been cleared following a retrial.
Colm Murphy, 57, from County Louth, was jailed for 14 years in 2002, but won an appeal against his conviction in 2005.
He was sent for retrial at the non-jury Special Criminal Court in Dublin in January.
In his verdict on Wednesday, Mr Justice Butler said interview evidence from members of the Irish police (gardai) was inadmissible.
Speaking after the hearing, Mr Murphy said: "I am glad to see it's all over.''
The original trial found Mr Murphy was guilty of conspiracy to cause an explosion because he lent mobile phones to the gang who planted the Omagh bomb, knowing they would be used in the bombing operation. He had always denied the charge.
During that trial, two gardai detectives were accused by a trial judge of consistent perjury in relation to interview notes.
That led to the Supreme Court quashing his conviction and ordering the retrial.
On Wednesday, Mr Justice Butler, sitting with two other judges, ruled that there was no evidence upon which the court could have convicted Mr Murphy.
He said the court had found that all of the evidence obtained in 15 police interviews with Mr Murphy following his arrest in February 1999 was inadmissible.
Last June, the Mr Murphy was one of four men found liable for the Omagh bombing in a civil action taken by 12 relatives of people killed in the attack.
Mr Murphy, Michael McKevitt, Liam Campbell and Seamus Daly, who are all alleged Real IRA members, were ordered to pay £1.6m in damages to the relatives. The civil case had no bearing on the retrial in Dublin.
A fifth man, Seamus McKenna, was cleared of liability.
Twenty nine people, including a woman pregnant with twins, died in the attack on 15 August 1998.
In 1984 Mr Murphy spent a year in jail in the United States for trying to buy missiles, rifles and submachine guns.
Omagh campaigner Michael Gallagher, whose 21-year-old son Aiden was murdered in the bombing, said the development came as a blow to bereaved families.
"It has been the history of this process that the families have been disappointed time and time again, but when it happens it is still hard," he said.
"But I think this is the first time in years I feel angry."
"This is a crime that the Taoiseach, the Prime Minister and the President of the United States took an interest in.
"If this can't be solved what hope is there for other crimes?"