The public accountability group Judicial Watch said Tuesday that a newly released document from the State Department shows that the agency may have deliberately tried to delay the discovery of Hillary Clinton's private email address.

That private email address led to the discovery of her own private server, which Clinton used to conduct business when she was secretary of state. It also led to fears that sensitive information on those emails may have been subject to cyberattacks on her less-secure home server.

Judicial Watch on Tuesday released a letter the State Department sent the group last week. State's letter said it has agreed to release a 2012 email that was sent to Clinton's private address.

"[U]pon 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," the State Department said in its April 18 letter.

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The Sept. 29, 2012, email is almost fully redacted, but it shows the email was sent to Clinton's private email address, " hdr22@clintonemail.com."

Judicial Watch says the State Department withheld that email in a Nov. 12, 2014, letter to the group, and argued that decision appears to be aimed at hiding Clinton's private email.

"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," said Judicial Watch President Tom Fitton.

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Clinton's use of a private email was first reported on March 1, 2015, nearly four months after State refused to give over the now unclassified email to Judicial Watch. Clinton offered her first public explanation of her use of a private email just days later, on March 10 of last year.

Fitton said the new disclosure shows that the State Department "acted in bad faith," and said it also gave Clinton more time to selectively delete thousands of emails on her server.

"One aim of our court-order discovery will be to get to the bottom of this cover-up," Fitton said.