"Investigators said content stored on the encrypted hard drive matched file hashes for known child pornography content"
Alright, so, the drive is encrypted and you don't know the content. You can't decrypt it yourself, or this case would be solved. So... file hashes of ENCRYPTED, THEREFORE SCRAMBLED files match child abuse content? Encryption (at least any modern, halfway decently made encryption, in case he made it himself) randomises the encrypted content, therefore you can draw exactly no conclusions from whatever the hash of that random string of characters comes out to.