A former FBI agent intends to plead guilty to leaking information about a foiled bomb threat to The Associated Press, the Justice Department said on Monday.

According to the Sept. 19 court filing made public Monday, back in 2012, Donald John Sachtleben, a government contractor who had worked as a bomb technician on cases like the Oklahoma City bombing, used his top secret clearance to gather information on a bomb the United States had intercepted from al-Qaida in Yemen. According to the document, Sachtleben then passed that information along to the AP thinking it was classified "secret."

Reuters reports that officials have called the leak "one of the most serious in U.S. history. The wire service adds:

"As part of a plea agreement filed in U.S. District Court in Indiana, Donald John Sachtleben agreed to a prison sentence of three years and seven months for the leak in addition to a separate sentence for unrelated child-pornography charges, the department said."

As we reported at the time, The Associated Press was the first to report the story, saying the bomb was a new, more sophisticated version of the kind al-Qaida tried to use during the failed Christmas Day bombing in 2009.

The big deal here is that the bomb was designed by al-Qaida's master bomb maker, Ibrahim Hassan al-Asiri, and the U.S. government had infiltrated al-Qaida, turning a would-be suicide bomber into an informant willing to turn over an intact bomb to the U.S. government.

As NPR's Dina Temple-Raston explained it, the reason the U.S. says this leak was damaging is because the informant "was actually a double agent" and Western intelligence agencies were hoping the agent could do more work. The leak blew the agent's cover.

The story also sparked a national conversation about the constitutional guarantee of a free press, when, during the investigation of the case, the Justice Department secretly obtained the phone records of AP reporters.

According court document released today, phone records obtained by investigators showed that Sachtleben called the AP reporter hours after he used his FBI-issued badge to "enter the examination space for the Explosives Unit."

"There can be no possible justification for such an overbroad collection of the telephone communications of The Associated Press and its reporters," AP President Gary Truitt said at the time.

In the end, the Justice Department decided to tighten the rules used to obtain records from the media.

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