* Backup logs that show hashes of files that match that of known child porn image files.
* Testimony from the guy's sister that she has seen him decrypting the drives, and that he showed her child porn from the drives.
So yes, what you're saying is true, but in this case, I'm (reluctantly) on the side of the authorities.
I agree with the poster below you that they should charge him if they do have that evidence.
But if they are holding him in contempt while waiting to force decrypt so that legal precedent can be set, or if they're holding him so that this way he is in jail without getting credit for time served on his potential cp charges, then this is all a pretty hefty abuse of due process and etc.
We really need to defend even the worst people's right to a decent correctional experience. Why?
Because if you are ever wrongfully imprisoned, you would want the same. And it really does happen!
Maybe next time they won't have evidence, but there's a handy encrypted drive to get someone with instead.