Convicted of unlawful sex with a 15 year old in 2000. Recently 'accused' of molesting the 2 year old child of a local barmaid, which is presumably where this so-called revenge attack came from. I expect that a man who has retreated from society to live in a caravan on the fringes of a run down estate is a pretty easy target for accusation, especially with a history of being on the sex offenders register.
I can't really find out too much about the attack from 2000, for which he sounds rightly punished. But you've got to be seriously worried about the mental capacity of anyone who wields a knife, and kills someone. Society isn't safe from that person no matter what right they thought they might be commiting.