WASHINGTON (AP) — The Justice Department has subpoenaed several witnesses to testify before a federal grand jury in Washington as part of its investigation into former CIA Director John Brennan, three people familiar with the matter said Monday.

The subpoenas were issued in recent days and represent an effort by the Justice Department to press forward with the investigation even as a Florida-based career prosecutor who'd been helping lead the inquiry left the case after expressing doubts about the legal viability of a potential criminal prosecution.

Joseph diGenova, a former Justice Department lawyer who served as a top prosecutor in the 1980s and later supported legal efforts by President Donald Trump to overturn his 2020 election loss, has since been sworn in to serve as a special counselor to the attorney general, and is expected to work on the investigation.

The months-old Brennan investigation is one of several criminal probes the Justice Department has opened over the last year against Trump's perceived adversaries. It centers on one of the Republican president's chief grievances — a U.S. intelligence community finding that Russia interfered on his behalf during his successful 2016 presidential campaign.

The subpoenas were described by people with knowledge of them who spoke on condition of anonymity to The Associated Press to discuss an ongoing criminal investigation. At least three were said to have been issued, said two of the people. CBS News earlier reported the issuance of subpoenas.

Brennan served as CIA director under President Barack Obama and was in that role when the intelligence community in January 2017 published an assessment detailing Russian interference aimed at helping Trump defeat Democratic nominee Hillary Clinton in 2016. An investigation led by special counsel Robert Mueller concluded that Russia meddled on Trump's behalf and that his campaign welcomed the assistance, but it did not find sufficient evidence to prove a criminal conspiracy.

The Justice Department last year received a criminal referral from Rep. Jim Jordan, the Republican chairman of the House Judiciary Committee, alleging that Brennan made false statements before the panel in 2023 about the preparation of the intelligence community assessment. Brennan and his lawyers have vigorously denied any wrongdoing and have called the investigation politically motivated.

The investigation has been unfolding for months in Florida, with investigators lining up interviews and issuing subpoenas for records. The latest subpoenas seek grand jury testimony in Washington, an indication that prosecutors expect they would have to bring any criminal case in Washington since that is where Brennan's testimony took place.

On Friday, it was revealed that a key national security prosecutor in Florida who'd been handling the investigation, Maria Medetis Long, left the case. She expressed doubts about the case and was removed, another person familiar with the matter said.

The Justice Department has tapped diGenova, 81, a Trump loyalist who served as the U.S. Attorney in Washington for part of the 1980s, to serve as a special counselor to the attorney general. He was sworn in Monday in Florida and is expected to work on the Brennan investigation.

DiGenova supported Trump's false claims that the 2020 election was stolen from him. He made headlines that year when he said Chris Krebs, a top Trump administration cybersecurity official who had determined that the 2020 election was free of major fraud or interference, should be killed. diGenova later apologized and a lawsuit filed against him by Krebs was withdrawn.

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Associated Press writer Alanna Durkin Richer in Washington contributed to this report.