As it happens, there's a reason law enforcement cannot use any tool as they see fit, at least within nations that uphold the rule of law.
And apparently, what the FBI used there violates the rule of law, which is why the judge threw out the idiots for trying.
But it's easy to guess what the FBI did: They infected the accused's computer with malware which also allowed the planting of (fabricated) evidence; like Hacking Team's "Galileo".
As a hint for future cases: If it's technology meant for espionage or warfare, it's probably not usable for law enforcement. If the evidence it creates is not tamper-resistant but actually opens more options for tampering, it's not usable for law enforcement. If you don't want to talk about, it's NEVER useable for law enforcement. If it comes with an NDA, it's NEVER usable by law enforcement.
It's not a double edged sword because of encryption, but because everything you do to foster surveillance will cut you, and everyone else, by jeopardizing security. Encryption is actually the scabbard.
Do you really want to be responsible for terrorists taking down the electrical grid, using a backdoor you inserted, or a vulnerability you kept secret, because you wanted your surveillance capabilities?
Yes, convicted for: - theft and pickpocketing - trying to form a union - tolerating homosexuality - rebellion (particularly if you were Irish) - being catholic in Ireland and owning a gun - circulating the works of Thomas Paine - mutiny with intent to increase workplace conditions - demanding voting rights for everybody - being an orphan - illegal duelling - being a woman baring herself for "an immoral purpose" - being a servant accused of theft - bigamy - clandestine marriage - poaching (including plants and fish).