@cstross Not just crimes, but also SIGINT. Worked example: in 2015, the NSA released William Friedman's papers. He retired in 1955 and died in 1969—but some of his papers were still withheld and others were redacted. And he filed a patent application in 1933 that for security reasons wasn't issued until 2003 (https://patents.google.com/patent/US6097812).