The State Department identified nearly 600 security violations in its now-completed review of email records of dozens of former agency officials and aides to former Secretary of State Hillary Clinton.

The investigation, which covered the 33,000 emails Clinton provided for review, found 91 "valid violations" attributable to 38 individuals, some of whom may face disciplinary action. Another 497 violations could not be tied to any specific person.

A nine-page unclassified report was sent to Iowa Republican Sen. Chuck Grassley, who is leading the congressional oversight of the security review, in a letter from Assistant Secretary of State for Legislative Affairs Mary Elizabeth Taylor dated Oct. 16.

The 36-month inquiry sought to determine "if any of the emails under review represented a failure to properly safeguard classified information" and whether any individuals could be determined to bear individual responsibility. Investigators reviewed thousands of documents, received hundreds of statements, and met with dozens of current and former State Department employees. The review was completed on Sept. 6.

The individuals under scrutiny were not identified, nor was it revealed if any of those who were found culpable were still employed at the State Department, per agency policy.

However, the list of State Department officials questioned reportedly included assistant secretaries of state responsible for U.S. policy in the Middle East, Europe, and Central Asia, as well as several ambassadors. It also included many current and former bureaucrats who passed along important messages to Clinton from outside officials.

A request for comment from the State Department was not immediately returned.

The State Department review began after the FBI investigated Clinton's use of an unauthorized server, hosted in the basement of her home in Chappaqua, New York, during her time as secretary of state from 2009 to 2013. Clinton insists the email set-up was simply a matter of "convenience."

The State Department review found "some instances" of classified information being "inappropriately introduced into an unclassified system in furtherance of expedience." But investigators uncovered "no persuasive evidence of systematic, deliberate mishandling of classified information."

Investigators faced several complications, as noted in the report. One issue was the "significant break-in time" — five to nine years — since an incident took place and therefore would not be fresh in people's memories. Another "serious" challenge was that there were people who were either unresponsive or unreachable. For former employees who remained elusive, any notifications of adjudication would be placed on file, and they have the opportunity to appeal the decision when they become aware of it.

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The State Department review began in 2015, but was placed on hold while the FBI conducted a criminal investigation into Clinton's use of an unauthorized email server during the 2016 election. In July 2016, former FBI Director James Comey publicly recommended that no charges be brought against Clinton or anyone else involved with her private email network, but he admonished Clinton and her team for being "extremely careless" in handling classified information.

All this played out while Clinton was a presidential candidate, and in late October the FBI reopened the investigation only to close it again days before the Nov. 8 election maintaining the same position Comey asserted months earlier. Clinton has often cited the FBI's handling of the emails investigation as one of the reasons why she believes she lost the contest to President Trump.

One of the main controversies stemming from Clinton's emails was how Paul Combetta, the tech aide who administered the server, deleted 33,000 emails despite a congressional order to preserve them. The FBI says it was only able to recover about 5,000 of the emails scrubbed by Combetta, and they were released in tranches up until earlier this year as part of a lawsuit brought by Judicial Watch. Clinton has said she "never received nor sent any material that was marked classified," but the FBI found 110 emails did contain classified information.

Last month Trump called the deletion of the emails "one of the great crimes committed" by Clinton.

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The State Department informed Congress over the summer that its review of the mishandling of classified information found 23 "violations" and seven "infractions" by 15 people. A "broad range" of disciplinary or administrative actions that could be taken include "counseling, reprimand, suspension, and/or separation," according to a letter in June from Taylor.

Later in June, Republicans called on the Democrat-led House Oversight Committee to hold a hearing focusing on the State Department's review, but so far have been ignored.

Clinton's security clearance was withdrawn in the fall of 2018 at her request, along with those belonging to Clinton's former chief of staff Cheryl Mills and others.