It's much simpler than that. A judge orders you to give police access to your account. Regardless of whatever labyrinthian setup you use to unlock the actual credentials, and barring a stay of the order pending appeal, if you do not give police access you will be held in contempt of court and you may be sent to prison until such time as you comply with the court order. Claims of "but technically I don't actually know the password" are going to impress a judge as much as an argument of "but technically it was the bullet that murdered him" would.