Doubt has been cast on forensic evidence gathered by the Colombian authorities against three Irishmen, who are in jail there on suspicion of aiding left-wing guerrillas.
Keith Borer Consultants of Durham was commissioned by the men's solicitor, Mr Peter Madden of Madden and Finucane, to examine the documentation produced so far.
One set of tests alleges that the clothes of the three, Mr Niall Connolly, Mr Martin McCauley, and Mr James Monaghan, showed traces of explosives and drugs.
They were detained travelling on false passports at Bogota Airport last August on suspicion that they had trained Revolutionary Armed Forces of Colombia (FARC) guerrillas.
The authorities argue that Mr Monaghan's clothes showed nitroglcyerine and tetryl explosive traces, and cocaine and amphetamines, while Mr McAuley's carried nitroglcyerine and nitro traces and cocaine.
The clothes of the third, Mr Connolly, who was Sinn Féin's representative in Cuba, reportedly responded positively to tests for DNT and ammonium nitrate explosives.
However, the accuracy of the tests has been challenged by Keith Borer Consultants, which said it was very unlikely that the men had been contaminated with explosives as suggested.
The US embassy in Bogota used an Ion Track instrument to test the clothes, which was "extremely sensitive, but not very discriminating", said Dr Keith Borer.
Later the Colombian State Laboratory re-examined the samples using a scanning electron microscope, gas chromatography, infra red spectroscopy and thin-layer chromatography.
"No positive results were obtained," Dr Borer said. "From this I can deduce that: (a) none of the tested samples had been close to a recently fired gun or residue from the same. Primer residue shows in electron microscopy at very low levels; (b) any organic explosives present were at a level lower than the detection limits of the test methods used. The tests used were not state-of-the-art for organic explosives, but still sensitive; (c) if ammonium nitrate was present, the level was lower than the detection limit of the method used.
"The method used, thin-layer chromatography, is very sensitive."
The mix of explosives allegedly found was "less usual", said Dr Borer, whose company has worked on the Oklahoma bombing inquiry and the investigation into the murder of the BBC presenter, Jill Dando.
"Nitroglycerine and ammonium nitrate are common. It is less usual to find DNT. It is even less usual to find tetryl or HMX.
"No evidence has been led to suggest that FARC has been using either of these.
"On the current evidence, it is my opinion that it is unlikely the three defendants were contaminated with explosives as suggested," said Dr Borer.
The British company is on a panel of experts accepted by the British government as qualified to give evidence in court on forensic matters.
