"Investigators said content stored on the encrypted hard drive matched file hashes for known child pornography content." If the disk is encrypted how can they match file hashes? Do they encrypt known CP files with the FileVault key and then compare? If so, isn't that enough to convict him?
Something doesn't add up in this story. Encryption and hashing are different processes with different algorithms - SHA vs MD5. For example, IPSec VPNs hash a packet with MD5 to prevent tampering, then encrypt the hash with SHA256 to prevent viewing. (Because the message could be modified while encrypted, were it not also hashed.) Isn't the point of encryption that it doesn't create a reliable hash - that 2 identical…
You do realize that MD5, SHA-1, and SHA-256 are all hashing algorithms? I highly doubt you meant a cipher built from a hash function (easy to do with Feistel net, though nobody does that), especially that IPsec doesn't define any such thing, from what I remember.
Given that you apparently don't understand how encryption and hashing work and relate to each other, you're not in a position to question the technical aspects of the story.