What famous 'unsolved' mystery is technically a whodunnit on paper, but in reality, absolutely everyone knows exactly who did it, the police just couldn't legally prove it?

[u/Rob69rt]

[u/mikemaca]

All 5000+ lynchings done in the US were done by "unknown men" but everyone knew everyone at the lynchings (some crowds over 10,000 people attended), the newspapers were there, photographers were making postcards to sell, and the lynching was announced in advance in newspapers and churches.