The man was charged with contempt of court under the authority given to the courts under the All Writs Act of 1789, the same law that federal prosecutors tried to use against Apple last year to force Apple to help decrypt a dead terrorist's iPhone. The former police officer was in jail for nearly 18 months. He will not be released until the judge lifts the order, or until the order is overturned on an appeal, or if he decides to hand over the decryption keys. The Electronic Frontier Foundation (EFF) has filed an amicus brief with the court in support of the appeal. The EFF requested the man be released from jail for two primary reasons.
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So it seems they had some other decent evidence that the computer had illegal content, and the court used that to justify requiring him to decrypt it. I wonder if receiving a package in the mail would be evidence enough to justify this on a DNM user?