Despite Doe’s refusal, f orensic analysts discovered the password to decrypt the Mac Pro Computer , but could not de crypt the external hard drives. [...] The Forensic examination also disclosed that Doe had downloaded thousands of files known by their “hash ” values to be child pornography. 3 The files, however, were not on the Mac Pro, but i nstead had been stored on the encrypted external hard drives. Accordingly, the files themselves could not be accessed.
I don't think it's unlikely at all, however, it is unlikely they would disclose having it for such a meaningless case.
The value of this case to them isn't decrypting the data -- it's in setting a precedent on forced data decryption, which they can then use for other cases.
Someone quoted this in a post below: "Prosecutors said Rawls has a lot of "chutzpah" to even ask to get out of jail while he appeals the contempt-of-court order to the Supreme Court, which has never decided whether forcing somebody to decrypt hardware amounted to a Fifth Amendment violation.", proving the point.
http://www2.ca3.uscourts.gov/opinarch/153537p.pdf
Despite Doe’s refusal, f orensic analysts discovered the password to decrypt the Mac Pro Computer , but could not de crypt the external hard drives. [...] The Forensic examination also disclosed that Doe had downloaded thousands of files known by their “hash ” values to be child pornography. 3 The files, however, were not on the Mac Pro, but i nstead had been stored on the encrypted external hard drives. Accordingly, the files themselves could not be accessed.