His brother Sean died in December 1975, when a landmine he was preparing for an attack on the British Army exploded prematurely. Another brother, Peter, served 14 years in prison for Provisional Irish Republican Army offenses. Yet another brother, Michael, went on trial in Vilnius, Lithuania, accused of trying to purchase arms and explosives for the Real IRA, was found guilty and sentenced to twelve years in jail, a conviction that was overturned with the defendant acquitted upon the completion of a retrial in 2013, largely due to the defence’s argument that Michael was the subject of entrapment, by MI5 agents.
Liam Campbell first came to the attention of the British and Irish security forces in the early 1980s and became the subject of an exclusion order in 1983 barring him from entering Northern Ireland.
Campbell was named by the BBC as one of the perpetrators of the 1998 Omagh bombing in a Panorama documentary.  He never faced criminal charges but was found liable for the bombing in a civil trial, along with Michael McKevitt, Colm Murphy and Seamus Daly.  The case, brought by relatives of the 29 victims, resulted in an award of combined damages of over £1.5m.
In May 2004, Campbell was convicted by a court in the Republic of Ireland for membership of the Real IRA and was sentenced to eight years imprisonment. In May 2009, he was arrested following the issue of a European Arrest Warrant at the behest of the Lithuanian authorities, where he was wanted in connection with a gunning running plot which saw his brother Michael arrested. Campbell remained in prison for four years and was released in 2013 following the decision of Belfast Recorders Court to deny Campbell's extradition to Lithuania. The court ruled that "[Campbell] was likely to be held in conditions which would be inhuman and degrading."
- "Vilnius 'Real IRA' trial to open". BBC News. 2009-08-18. Retrieved 2009-08-18.
- "Michael Campbell Released From Prison In Lithuania".
- "Lithuanian court clears Irishman in Real IRA case".
- "Michael Campbell freed by Lithuanian court".
- "Dáil Éireann - Volume 345 - 25 October, 1983". Retrieved 2007-02-12.
- Hopkins, Nick (2002-07-27). "The five suspects families want to bring to court". London: The Guardian. Retrieved 2007-02-12.
- The men sued by the Omagh families, BBC News, Monday, 8 June 2009.
- "Four found liable for Omagh bomb". RTÉ News. 2009-06-08. Retrieved 2009-06-08.
- "Omagh bombings case: the European Court of Human Rights gets it wrong, again". The Telegraph. Retrieved 21 November 2014.
- "Extradition bid Omagh bomber is free again - BelfastTelegraph.co.uk". BelfastTelegraph.co.uk. Retrieved 2015-12-15.
- "COURT RULES EXTRADITION WOULD BREACH ARTICLE 3 OF THE EUROPEAN CONVENTION ON HUMAN RIGHTS". Belfast Recorders Court. January 16, 2013.
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