I don't think the police will have to look very far

To find the people responsible for the Birmingham pub bomb in 1974. Despite their convictions being quashed in 1991, it was well known by those close to the investigations that the original convictions were correct. And that is borne out by the fact that the case was not reopened after the successful appeal case.
I cannot even guess what the motive might be to reopen a case now especially as there isn't any real new evidence. The statement by the West Midlands Police merely says that they want forensic experts to examine potential new evidence.
I can only surmise that there is a political motive linked in some way to the cowardly politics of appeasement that led to the 6 IRA scum being released by the Court Of Appeal.
It will be interesting to see how the West Midlands Counter Terrorism Unit talk themselves out of the situation when the forensic investigation proves that the original convictions were sound. But my bet is that nothing will be heard of this ever again.