Another name to research is Bill Binney. He was in the NSA until 2001, the technical director from 1997 until 2001, and became an outspoken whistleblower regarding the surveillance of American citizens. He created the NSAs Thinthread program which they scrapped in favor of a contractors "Trailblazer", which he describes as a "bastardized version of Thinthread" that removed all the encryption of Thinthread.

https://www.computerweekly.com/feature/Interview-the-original-NSA-whistleblower

He alleges:

The NSA buried key intelligence that could have prevented 9/11;

The agency’s bulk data collection from internet and telephone communications is unconstitutional and illegal in the US;

The NSA is ineffective at preventing terrorism because analysts are too swamped with information under its bulk collection programme;

Electronic intelligence gathering is being used for covert law enforcement, political control and industrial espionage, both in and beyond the US;

Edward Snowden’s leaks could have been prevented.

He spoke often during FISAgate but havent heard much from him lately.