The prosecution at Mr Danny McNamee's trial painted a false picture of him as the master bomb-maker behind the Hyde Park bombing in 1982, the Court of Appeal in London heard yesterday.
Mr Michael Mansfield QC, counsel for Mr McNamee, who was convicted in 1987 of the bombing which killed four members of the Household Cavalry, said: "We say it was known to be a false picture by the prosecuting authorities at the time."
Mr McNamee (38) listened intently as Mr Mansfield began an attempt to clear his name at the start of the hearing. Material had been kept from him at his trial and his failed appeal in 1991, said Mr Mansfield.
Mr McNamee, from Crossmaglen, Co Armagh, was sentenced to 25 years in 1987. He was recently released from the Maze Prison under the terms of the Belfast Agreement. He has eight grounds of appeal.
Mr McNamee's case was referred back to the Court of Appeal by the Criminal Cases Review Commission after inquiries into several issues, including disclosure of evidence at the time of his trial, and scientific and fingerprint evidence.
At his Old Bailey trial the prosecution alleged that the physics graduate was the "master bombmaker" behind the Hyde Park bombing. He was convicted of conspiracy to cause explosions.
Mr Mansfield said yesterday that fresh evidence concerning convicted bomb-maker Desmond Ellis substantially undermined the prosecution case and supported Mr McNamee's defence. He said Ellis was the source of a "significant proportion" of the fingerprints found on devices with "explosive significance in the case."
The Crown's case against Mr McNamee was that his participation in a conspiracy to cause explosions in the UK between January 1st 1982 and January 26th 1984 could be inferred from the presence of his fingerprints on three items:
The non-adhesive side of a piece of red tape wrapped round an encoder for use in a radio-controlled explosion found in an arms cache at Pangbourne Woods, Berks, in October 1983.
The adhesive side of a piece of grey tape wrapped around part of a radio receiver for the same use found at Salcey Forest, Northants, in January 1984.
The gold tip of a Duracell battery used in a time and power unit, detonated by the bomb squad after being found in Phillimore Gardens, west London, in December 1983.
Mr Mansfield revealed that circuit boards with identical "artwork" to those which had formed such a significant part of the case against Mr McNamee had been found in Ellis's possession in 1981.
He submitted that if the information concerning Ellis had been known to Mr McNamee at his trial, it would have "considerably strengthened" his case that the fingerprints attributed to him were less consistent with bomb-making and more consistent with innocent contact within the electronics factory where he worked.
During the appeal, counsel will also submit that fresh expert evidence was now available that the fingerprint impression recovered from the Duracell battery in the explosive device found in Phillimore Gardens could not be shown to be that of Mr McNamee.
The hearing continues today.