Counselor and Chief of Staff to Hillary Clinton, Cheryl Mills speaks onstage at the Cinema For Peace event benefitting J/P Haitian Relief Organization in Los Angeles held at Montage Hotel on January 14, 2012 in Los Angeles, California. Michael Buckner/Getty

WASHINGTON (AP) — Hillary Clinton's former chief of staff, Cheryl Mills, and two other staff members were granted immunity deals in exchange for their cooperation in the now-closed FBI investigation into Clinton's use of a private email server as secretary of state, says a Republican congressman.

Rep. Jason Chaffetz, chairman of the House Oversight and Government Reform Committee, told the Associated Press on Friday that Mills gave federal investigators access to her laptop on the condition that findings couldn't be used against her.

Chaffetz said he was "absolutely stunned" that the FBI would cut a deal with someone as close to the investigation as Mills.

"No wonder they couldn't prosecute a case," Chaffetz said. "They were handing out immunity deals like candy."

A yearlong investigation by the FBI focused on whether Clinton sent or received classified information using the private server, which was not authorized for such messages.

FBI Director James Comey said in July that his agents hadn't found evidence to support any criminal charge or direct evidence that Clinton's private server had been hacked. He suggested that hackers working for a foreign government may have been so sophisticated they wouldn't have left behind any evidence of a break-in.

The FBI had already said it granted immunity to Bryan Pagliano, a tech expert who set up Clinton's email server, as well as Paul Combetta, a computer specialist.

Chaffetz said in addition to Mills, others granted immunity include John Bentel, then-director of the State Department's Office of Information Resources Management, and Clinton aide Heather Samuelson.

Chaffetz said he is looking forward to asking Comey questions about the immunity deals when Comey testifies Wednesday before the House Judiciary Committee. Chaffetz, R-Utah, is also a member of that committee.