I take it that you mean the UK when you say the Double jeopardy protection..well there is the fact that as tecnoledgy advances more and more people are being found out to be the real killers..that law is only good for the guilty. If a killer of three people has got away with murder by being found not guilty, and new tech proves he really was the killer ...he should be tried again on further charges...if it were your family members with the murdered we would not be having this conversation.
Be well Ian