Like Hancho said. It is their job to build the case with all available evidence. If they cannot do that on their own merit it is their problem. Giving up a pw in my mind is the same as making a self-incriminating statement and that falls under the 5th amendment.
As far as the different crimes go...when you start choosing who is protected and who isn't, pretty soon none of us will be. Precedents have already been sent that are taking us in that direction.