Raedwulf, I agree that justice is not rigorous enough. You are also quite right to say that positing deterrence against justice is bollocks. In fact, efficient efficient law enforcement and a thorough justice system are much better deterrents.
CP will never return to Britain. After the experience of the seventies - when bomb explosions were followed by arrests of hapless Irishmen - most of us know that justice can effectively quickly be surrendered to a lynch mob mentality. It took me a long time to realise that the Maguires were innocent, that the Guilford Four were innocent and that the Birmingham Six were innocent. I am not proud of that. Thank God we didn't top them.
Justice is always administered by fallible people. There always have been mistakes and I can't see that changing. In the USA, student lawyers and journalists have freed people from Death Row whom the professionals failed to save. I would oppose the death penalty anyway - even if the system did not make mistakes. It does though.