The people who are protected by this rule are the guilty who are wrongly declared innocent; the murderer whose voice couldn’t be identified on the tape; the rapist who couldn’t be identified because DNA testing wasn’t sufficiently developed at the time; the robber who couldn’t be identified because facial mapping technology didn’t exist to show their face beneath the mask. People may in unguarded moments confess to crimes for which they have been found not guilty. Why would the state be in their favour and against the victims that so deserve justice - why should victims suffer because evidence didn’t emerge until later?  The test for guilt will still be 'reasonable doubt' - defendents who are genuinely innocent have no need to fear because they will still be found innocent.