This seems extremely unlikely in practice considering how many people would need to play along. Also what happens if more evidence appears afterwards or the act

This seems extremely unlikely in practice considering how many people would need to play along. Also what happens if more evidence appears afterwards or the actual killer gives himself up? You just end up playing whack a mole to keep the lie working. No it really doesn't make sense. Not saying it's impossible but in those cases they need to A) know who the real killer actually is, and B) kill/suicide the fall guy.