My guess also..... per Horowitz report! The opening pages of the transcript provide a lot of clues as to who the unnamed Supervisory Special Agent working from a field office that traveled to the UK, fired Steele for unprofessional conduct, and was still working for an FBI field office .... FTA:  "However, a review of Horowitz's findings leaves little doubt that the unnamed SSA is Joe Pientka -- someone who could soon play a prominent role in the ongoing prosecution of Michael Flynn, as the former Trump national security adviser fights to overturn his guilty plea on a single charge of making false statements. Specifically, Horowitz's report states that "SSA 1" was one of the FBI agents to interview Flynn at the White House on Jan. 24, 2017, in a seemingly casual conversation that would later form the basis for his criminal prosecution. It was previously reported that the interviewing agents were Peter Strzok, who was later fired by the FBI for misconduct and anti-Trump bias, and Pientka, whom Strzok previously identified as his notetaker for the Flynn interview. Flynn's attorney has also mentioned Pientka's role during past court proceedings. Of the two agents, only Strzok is openly named in the Horowitz report, which strongly indicates that the other is Pientka."