The Birmingham Six, The Maguires and The Guilford Four were all arrested and found guilty of causing explosions. There was forensic evidence offered against them. That forensic evidence was later discredited. Seventeen innocent people spent years in prison. One of the Guilford Four died in prison - I may well have forgotten others. Whole families were devastated. It brought no closure for the victims of the bombings, because the culprits were no longer pursued.
The science of today becomes the fallacy of tomorrow. Science is never absolute. It only tells us what we know now. By ddw's reckoning, we should have broken seventeen innocent necks in the seventies. Thank God this hideous little ritual of revenge no longer takes place in most civilised countries.