Some of the emails on Hillary Clinton's server were reportedly so sensitive that investigators initially didn't have clearance to view them
Hillary Clinton listens to a question as she testifies before the House Select Committee on Benghazi, on Capitol Hill in Washington, October 22, 2015.
Some of the information that passed through Hillary Clinton's private email server was so sensitive that high-level officials examining the account had to get special security clearance before they could proceed with their probe, NBC's Ken Dilanian reported on Tuesday.
That is according to an intelligence official familiar with the probe into the former secretary of state's "homebrew" server, which is being led by the intelligence community's inspector general, Charles McCullough.
The FBI has also been looking into whether classified material was mishandled during Clinton's tenure at the State Department from 2009 to 2013.
Some of the emails found on Clinton's account — according to a letter McCullough sent to senior lawmakers on January 14 and obtained by Fox News and other publications — contained intelligence so sensitive that it has since been allocated to a special-access program (SAP) designation.
SAPs are designed to safeguard information deemed more sensitive than even "top secret."
"The special access program in question was so sensitive that McCullough and some of his aides had to receive clearance to be read in on it before viewing the sworn declaration about the Clinton emails," Dilanian reported.