WASHINGTON – FBI Director James Comey told Congress on Tuesday that his agency granted immunity to Hillary Clinton’s former chief of staff because agents wanted to inspect her laptop as part of a now-closed FBI investigation into Clinton’s use of a private email server as secretary of state.

The immunity deal for Cheryl Mills was limited to information contained on her laptop, Comey told a Senate committee, adding that the FBI’s collective judgment was that “we need to get to that laptop.”

Comey told Sen. Ben Sasse, R-Neb., that Mills was acting as a member of Clinton’s legal team in the case. He said the FBI decided it would take too long to try to force Mills to turn over the laptop without an immunity deal.

Trying to obtain the laptop though a grand jury or other method “would likely tangle us up” in arguments over legal privilege “for a very long time,” Comey said.

Sasse and other Republicans have said they were surprised that the FBI would cut a deal with someone as close to the investigation as Mills. By including the emails recovered from the laptops in the immunity agreements, the Justice Department exempted key physical evidence from any potential criminal case against Mills and other aides.

Republicans have assailed Comey’s decision not to prosecute Clinton, the Democratic nominee for president. Several have demanded the Justice Department investigate whether Clinton lied during testimony last year on the deadly 2012 attacks in Benghazi, Libya. Democrats call the claims partisan and intended to hurt Clinton’s candidacy.