Prominent republican Colin Duffy, currently held over the murder of a Northern Ireland prison officer, is at the centre of a challenge to the European Court of Human Rights which could force a change in the laws governing the length of time terror suspects can be held.
Duffy, 44, from Lurgan, Co Armagh, who has been cleared of murder charges on three separate previous occasions - was arrested last week in connection with the killing of David Black.
Mr Black, a 52-year-old father of two, was gunned down during a high speed ambush on a motorway as he drove to work at Maghaberry high security prison on November 1.
Under the Terrorism Act 2000, suspects can be held in custody for up to 28 days before either being formally accused or released. The powers have been in force for more than a decade and have been repeatedly approved by MPs.
In April a panel of three senior judges in Belfast, including Lord Chief Justice Sir Declan Morgan, agreed to the challenge from Duffy and three unidentified others.
Lawyers for the men argued that during a murder inquiry into the deaths of two soldiers at Massereene military barracks in Antrim during 2009, the UK authorities breached Article 5 of the European Convention, which says suspects should be brought before a judge "promptly" and tried within "reasonable time".
He has already failed to win a Supreme Court challenge based on human rights.
Duffy has been cleared of terrorism charges on three separate occasions. He was jailed for life in 1995 for shooting dead a former Ulster Defence Regiment soldier, John Lyness, but the conviction was overturned at the Court of Appeal a year later.
In 1997, he was charged with shooting dead two Royal Ulster Constabulary constables in Lurgan town centre. The charges were later dropped.
Last January Duffy was acquitted of murdering Sappers Patrick Azimkar, 21, and Mark Quinsey, 23 in March 2009.