He ran FBI Counterintelligence. Horowitz says he opened Crossfire Hurricane. He told the Inspector General he skipped a defensive briefing so a target would not change tactics. Handwritten notes in the Flynn file ask whether the goal was truth, or to get him to lie so they could prosecute him or get him fired.
E.W. Bill Priestap. Federal Bureau of Investigation official portrait, 28 January 2015. U.S. government work (PD-USGov-FBI). Wikimedia Commons File:Edward_W._Priestap.jpeg.
Horowitz: AD E.W. “Bill” Priestap opened the case after friendly-foreign-government information. Consensus of senior officials. Not a court. Not dumped again as the lead card below.
The rest of the file
J. Edgar Hoover FBI Building. Ajay Suresh. CC BY 2.0. FBI named him AD of Counterintelligence.