The Birmingham 6, The Guilford 4 and The Renault 5 were as guilty as (to quote Blackadder) a puppy sitting next to a pile of poo.
They got off because (re: released) due to evidence, as you say, of police tamperring. It was a mistake of the police, there was actually enough evidence to convict them anyway. The authorities just wanted it to stick as, this time, the IRA were fairly good at coverring their tracks.
Hanging terrorist scum, whether muslim or IRA is not only a good thing, but cathartic and necessary for a civilised society.
May terrorist scum, particularly those with beards and no moustaches rot in hell with no pornography or Jaffa Cakes.