THE ferocity of their own attack caught out Nelson and Gordon.
They left Patrick Butler's blood all over one corner of Nelson's cell and on their clothes.
The pair changed into new garments after the attack and denied they had been wearing the stained items.
But they were linked to the stained clothes by DNA testing.
Blood splashes were also found inside a trouser fold where it simply could not have landed unless Nelson had been wearing them.
The ferocity of the attack, on an apparently genial but vulnerable man, also convinced prisoners to give vital eyewitness evidence - which is very rare.
One, given the pseudonym "Stephen Andrews", told the court: "I felt appalled at what happened to Patrick Butler. Disgusted."
Nelson, himself, said he was surprised and devastated' when he found prisoners were prepared to give evidence.
The prisoners who gave evidence were probably already not enamoured of the pair because they were outsiders in a north west jail.
They said Gordon had a gold tooth and strutted around, while Nelson only wore nice clothes - the prosecution alleged some may have been given to them by other prisoners to pay off drug debts.
And their defence, that three other men carried out the attack, was too light on details to be plausible.
It sounded exactly what the prosecution called it: "A monstrous invention, and a very late invention."
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