Lawyers for indicted former Perkins Coie partner Michael Sussmann want one of his former clients to be granted immunity to testify in his defense, accusing Special Counsel John Durham of improperly blocking the client’s testimony by suggesting he may face criminal exposure from Durham’s probe.

Sussmann’s lawyers say the former client, technology executive Rodney Joffe, would offer “critical exculpatory testimony,” including testifying that his 2016 research into alleged ties between then-candidate Donald Trump and Russia was not related to Hillary Clinton’s campaign.