Many people have been convicted of historical offences, I'm no investigating officer so do not know how they manage to prove these things or the way the law are able to put forward evidence against someone, but there are many cases that have resulted in successful convictions years even decades after the initial crime, so if proof is there then there is no reason to arrest, and in the case of Bill Roach they do say they have enough proof to charge him with the offence.
Alison