Maria Medetis Long, a top prosecutor in the US Attorney's Office in Miami, informed attorneys connected to the investigation late on Thursday that she is no longer working on the case, the sources said. The probe is examining whether Brennan made false statements in 2023 congressional testimony about the US intelligence finding that Russia interfered in the 2016 election to aid Trump.
It was not immediately clear what led to Medetis Long's removal from the probe, which was first reported by CNN. The investigation has been ongoing for months.
A Justice Department spokesperson confirmed the move and portrayed it as routine DOJ practice.
"Attorneys are moved around on cases so offices can most effectively allocate resources," the spokesperson said in a statement. "It is completely healthy and normal to change members of legal teams."
Reuters reported on Thursday that the FBI was planning to interview roughly a half-dozen witnesses, including former US intelligence officials, over the next several weeks as part of the investigation into Brennan.
Brennan, a cable news analyst and longtime critic of Trump, has condemned reported investigations into him as politically biased and a misuse of the legal system. His lawyer has said there is no legal basis for an investigation.
A DOJ official told Reuters on Friday that there had been frustration inside the department with the pace of the investigation.