'It is likely that no one will now be successfully prosecuted'

Although Sean Hoey was the first man to face murder charges over the Omagh bombing, a number of other individuals have been directly or indirectly linked to the atrocity.

In March 2001, the families of the 29 victims launched a civil suit for damages against the Real IRA, which admitted to the blast, and five men - Hoey was not among them - whom they named as being responsible.

The following year, one of the men, Colm Murphy, a 48-year-old builder and publican from Co Louth, was found guilty by the Dublin special criminal court of conspiracy to cause an explosion and was jailed for 14 years.

Three years later, however, he successfully argued that his conviction was unsafe and is currently awaiting a retrial.

Investigators on both sides of the border have struggled to amass evidence against the other suspects.

Seamus Daly, another of the five men named, was found guilty of being a member of an illegal organisation in February 2003, and served more than three years in prison in the Republic. It is alleged that mobile phone records show Daly, from Co Monaghan, was in Omagh shortly after the bombing.

In in 2003, Michael McKevitt, understood to be the leader of the Real IRA, was jailed by a Dublin court for 20 years for "directing terrorism", although the trial judge was explicit that the charges were unrelated to Omagh.

McKevitt, whose wife, Bernadette Sands McKevitt, is the sister of the iconic hunger striker Bobby Sands, is a former IRA quartermaster who quit in disgust at the peace process.

Neither of the other two men named by victims' families, Liam Campbell and Seamus McKenna, has faced charges in connection with the murders, though Gardai froze €1m in assets belonging to Campbell in 2002.

Another man, Anthony Joseph Donegan, from Dundalk, appeared in court in 2005, accused of supplying the maroon Vauxhall Cavalier used in the bombing, but was released when the charge was dropped on the orders of the Irish Public Prosecution Service.

A 2001 report by the Northern Ireland police ombudsman, Nuala O'Loan, accused the force of hundreds of failures in the lead-up to the bombing and the way it was investigated.

The report detailed warnings that were received and ignored, key suspects who were never interviewed and critical information that was not passed on.

The then PSNI chief constable, Sir Ronnie Flanagan, dismissed the report as erroneous and "a denial of natural justice", but the families of the victims believe that such failings, and a desire on both sides of the border to protect informants, led to the investigation running into the sand.

With Hoey's acquittal, they believe it is likely that no one will now be successfully prosecuted in connection with the bombing.