Hear hear Caligula,
They were convicted on the basis of something called the Griess test. If you had been in contact with nitroglycerine, your hands would come up blue in tests.
Hence the importance of the evidence of Dr Skuse, the Home Office pathologist whose 'Griess test' identified nitroglycerine on the hands of five of the men. It has subsequently emerged that similar results can be obtained from handling tobacco, playing cards, even using soap.
They forgot to mention that all the witness in the case said that they saw Gerry Conlon playing cards they also forgot to mention the fact that playing cards are coated in a substance that gives the same positive test. Funny that.