The State Department withheld an email that would have shown — months before it was eventually reported — that Hillary Clinton used a personal email account to conduct State Department business, a conservative watchdog group claims.

Update: The State Department said in a statement after publication on Tuesday that the court filing referenced below contained an administrative error and that the dates listed in the document sent to Judicial Watch were inaccurate. The agency’s statement is listed below the original article.

Judicial Watch says that it received a letter from the State Department last week in which agency officials said that a September 2012 email had been completely withheld from a production of documents that the watchdog demanded as part of a Freedom of Information Act seeking records containing Benghazi talking points.

“Also, upon further review, the Department has determined that one document previously withheld in full in our letter dated November 12, 2014 may now be released in part,” reads the new letter from the State Department.

The Sept. 29, 2012 email is entitled “Key Points” and was sent among Clinton and two of her top aides, Cheryl Mills and Jake Sullivan. It concerned talking points that Clinton planned to use for a conference call with a group of Senators.

The heavily-redacted email contains one key piece of information: Clinton’s personal email address, HDR22@clintonemail.com.

Judicial Watch contends that Clinton’s off-the-books email arrangement would have been revealed much sooner it eventually was if the State Department had turned over the email instead of withholding it in full.

“If the State Department disclosed the email when first supposedly found, Clinton’s email server and her hidden emails would have been disclosed nearly two years ago, before Clinton authorized the alleged deletion of tens of thousands emails,” the group stated in a press release.

The New York Times broke the story of Clinton’s exclusive use of a personal email account last March. Days later, The Associated Press reported that Clinton’s email account was hosted on a private email server that she kept at her New York home.

While it was revealed in 2013 that Clinton used HDR22@clintonemail.com while in office, it was not known that she did so exclusively until The Times report. State Department attorneys who were collecting documents for the House Select Committee on Benghazi in the summer of 2014 reportedly noticed Clinton’s personal email address listed on a batch of official emails.

The State Department then set out on a months-long process to request Clinton’s work-related emails. Negotiations started in July 2014, and Clinton finally turned over the 30,000-plus pages of records on Dec. 5.

[dcquiz] In the meantime, Clinton’s attorneys sifted through her emails and pulled out those they deemed not to be work-related. They also appear to have crafted a set of talking points for Clinton to use to defend her unorthodox email system.

“Now we know the Obama administration consciously refused to give up key information about Hillary Clinton’s email in 2014. It covered up this email both from the court and Judicial Watch,” Judicial Watch president Tom Fitton said in a statement.

“This cover-up provided Hillary Clinton enough time to hide potentially thousands of government records.”

A State Department official released a statement to the Washington Free Beacon which reads:

The State Department generally does not comment on matters in litigation. Here, however, there is confusion arising from an administrative error in recent correspondence in which the Department said that the document in question was withheld in November 2014. That is incorrect. The complete facts surrounding this document are set forth in a public court filing from July 2015. As described in the attached filing, the Department received the document in June 2015 from members of former Secretary Clinton’s senior staff, and did not withhold it until that time. The Department regrets any confusion and will be sending corrected correspondence to Judicial Watch.

Judicial Watch’s Tom Fitton responded with another statement.

“Evidently, the State Department can’t track their cover ups,” he said. “This is why we have discovery.”

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