<https://www.msn.com/en-us/news/politics/exclusive-trump-raid-documents-could-reveal-intel-sources-on-us-payroll/ar-AA10Bgwh

Some of the notes, which Comey locked in a safe, cited classified sources and methods,including the identities of witnesses and informants along with the code names their FBI handlers assigned to them, according to federal court papers. They also document the assistance provided by foreign intelligence agencies.

https://www.realclearinvestigations.com/articles/2019/07/22/comey_under_scrutiny_for_own_inquiry_and_misleading_trump_119584.html