Comment by mjolk

The defendant provided the password to his iphone (that contained highly-unsavory media of his nieces), which contained an unlock code for his laptop (filevault backup decrypt key). He connected the external drives to this laptop, and when he'd transfer media from his laptop to the drives, logging would occur with the file checksums. The hash/checksum is on the laptop with the filepath to the identified external drives, and because the hashes match known media of child victimization, the prosecution knows exactly where the evidence exists on the drive, once decrypted.