Who knew? Not me. The FBI does not discuss its operations with other agencies of the US Government. Period. I made liaison with the FBI on many occasions when I was with DIA and they were always careful to make it clear that whatever you might give them in the way of information they would give you exactly nothing in return. In retirement from government I have often observed the FBI working in support of DoJ in court cases.
It has always been my understanding that when the FBI investigated you they searched through records, listened to your telephone, read your E-mail and in the end interviewed you.
Now I learn that they also recruit "confidential sources" to speak to you about the subject of FBI interest WITHOUT bothering to inform you that they are going to tell the FBI what you said about things. Some of these "confidential sources" are employed by the FBI for long periods of time. The American professor now teaching at a UK university who was sent by the FBI to talk to several Trump campaign people was one such. Other "confidential sources" are recruited for a particular case Sometimes they are recruited from among the existing acquaintances or "friends" of the person targeted by the FBI. In other words if DoJ, the WH, or the Bureau (FBI) want to know what I, or anyone else, really says about a given topic, they can recruit someone I know using pressure, persuasion or money to "rat" me out.
Felix Dzerzhinsky would have been proud of their skills if they had been his men. pl