Federal Judge Emmet Sullivan has appointed an independent prosecutor to delve into President Donald Trump‘s former national security adviser Michael Flynn. The move was designed to discover whether the Justice Department’s move drop the Flynn case was a made for political reasons.

Flynn initially pleaded guilty to lying during a questioning on Russia’s meddling in the 2016 elections. He later attempted to deny his claims and drop his guilty plea. The president and his supporters urged the Justice Department to drop the case, which raised suspicion about the potential politicization of the matter. Attorney General William Barr has been accused of promoting Trump’s interests ahead of the law, a fact that spurred Sullivan to call for external help.

The newly hired prosecutor, Judge John Gleeson, served in the Eastern District of New York. He has been asked by Judge Flynn to analyze the case and evaluate the possibility that Flynn’s actions may qualify as perjury.

Sullivan wrote a op-ed for the Washington Post about the irregularities of the Justice Department’s actions in the case. “There has been nothing regular about the department’s effort to dismiss the case,” he wrote, “the record reeks of improper political influence.”