Because that's the way it is. There's a doubt you did it, but it's still probably you and the police aren't looking for any body else.

I think there's a move afoot in the UK to remove or modify the double-jeopardy protection when new evidence turns up.

In the US there is State and Federal court procedure. The LA policemen who were acquitted of assaulting Rodney King in a State Court were later found guilty of infringing his civil rights in a Federal Court.

(Or something, not being an expert on the exact charges...)

Paul