Bryan Pagliano, the technology aide to Hillary Clinton who was granted an immunity deal during the FBI's investigation of the server system he helped create, refused to appear at a House Oversight Committee hearing Tuesday and ignored a subpoena to produce a copy of his immunity agreement with the Justice Department.

"His attendance is required here today," Rep. Jason Chaffetz, chairman of the committee, said of the IT aide.

Rep. Trey Gowdy questioned why Pagliano would decline to appear if his testimony is protected by his immunity agreement with the Justice Department.

"If he's been immunized, and you can't prosecute anyone for anything, where's the liability for him coming and answering questions?" the South Carolina Republican asked.

Paul Combetta, an employee of Platte River Networks, exercised his Fifth Amendment rights and refused to answer questions about his firm's involvement in the deletion of Clinton's emails despite the existence of a preservation order for those records.

The immunity deal extended to Combetta came as a surprise to lawmakers when it was revealed by the New York Times last week.

Combetta deleted thousands of Clinton's emails in March 2015, after the former secretary of state's private server became a subject of political controversy.

Bill Thornton, a Platte River Networks specialist, also exerted his Fifth Amendment rights and refused to respond to questions about whether he was interviewed by the FBI in its investigation of the private email network his firm maintained.

Notes made public by the FBI on Sept. 2 indicated Pagliano was warned that the server he built would likely house classified material, but he operated the network for four years from his position in the State Department's IT office anyway.

The House Oversight Committee hearing was the third in the past week that examined aspects of Clinton's email network.

Chaffetz said the committee would weigh options of how to deal with Pagliano's refusal to appear after the hearing concluded.