It's a tool, not the only tool. If you have a population of 100M, even if 1M match, then you add geographic area, skin colour, hair colour/style, height, known

It's a tool, not the only tool. If you have a population of 100M, even if 1M match, then you add geographic area, skin colour, hair colour/style, height, known criminality, ... suddenly you're down to enough people you can investigate. Sure, if your police/justice system is not competent you have a problem, but you had that in the first place.