TIL that in a 2017 criminal case, the US government put the secrecy of its hacking tools above all else. Prosecutors chose to drop all charges in a case of child exploitation on the dark web rather than reveal the technological means they used to locate the anonymized Tor user.

https://arstechnica.com/tech-policy/2017/03/doj-drops-case-against-child-porn-suspect-rather-than-disclose-fbi-hack/