IANAL, but isn't there something about the rules of evidence? Like, the prosecution can't just say "we think he hid it on an encrypted HDD, but we aren't sure"

IANAL, but isn't there something about the rules of evidence? Like, the prosecution can't just say "we think he hid it on an encrypted HDD, but we aren't sure". The judge won't allow that. But if you claim to have forgotten the password, then the prosecution can speculate.