Story highlights The Pentagon threatens legal action against the author

It says Matt Bissonnette has violated secrecy agreements he signed

Bissonnette says he was one of the SEALs who finished off bin Laden

Bissonnette was a chief petty officer when he left the Navy

The Pentagon general counsel threatened legal action Thursday against a former Navy SEAL who wrote a revealing book about last year's Osama bin Laden raid, warning him he has violated secrecy agreements and broken federal law.

In a letter addressed to "Mark Owen," the pen name of book author Matt Bissonnette, General Counsel Jeh Charles Johnson wrote the Pentagon is considering pursuing "all remedies legally available" against the former SEAL and his publisher, Penguin Putnam.

"In the judgment of the Department of Defense, you are in material breach and violation of the nondisclosure agreements you signed. Further public dissemination of your book will aggravate your breach and violation of your agreements," Johnson wrote.

The book is called "No Easy Day" and is a gripping account of the Navy SEAL raid on bin Laden's compound in Pakistan last year that ended in the death of the world's most notorious terrorist leader.

The story sheds more light on the now famous skill and daring of the SEALs. But the book's very existence stoked controversy because members of the elite unit don't usually divulge details of their operations.

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The book is one of several accounts about the operation to have surfaced after last year's raid.

Government officials only recently became aware the former SEAL was writing a book, but they were told it encompassed more than just the raid and included vignettes from training and other missions.

They wanted to see a copy, a Defense Department official said, to make sure no classified information would be released and to see if the book contained any information that might identify other team members.

Thursday's letter to Bissonnette came after a department review of the book.

Bissonnette wrote in the book that he was part of a team heading up a stairwell in search of bin Laden, forces led by a SEAL point man.

"We were less than five steps from getting to the top when I heard suppressed shots.

"BOP BOP.

"The point man had seen a man peeking out of the door on the right side of the hallway about ten feet in front of him. I couldn't tell from my position if the rounds hit the target or not."

They went into a room and saw two women standing over a man at the foot of a bed, "hysterically crying and wailing in Arabic."

One of the women shouted in Arabic and moved toward the point man.

"Swinging his gun to the side," the point man grabbed the women and moved them to a corner.

"If either woman had on a suicide vest, he probably saved our lives, but it would have cost him his own. It was a selfless decision made in a split second," Bissonnette wrote.

Bissonnette described how he and another SEAL entered the room and saw the man, clad in a white sleeveless T-shirt, loose tan pants and a tan tunic, twitching and convulsing. The author said he and another SEAL finished him off with several rounds and soon after identified him as the notorious leader of al Qaeda.

The killing occurred even though a government lawyer told the SEALs that if bin Laden didn't pose a threat, he should be detained.

The author found two empty firearms during a search of the area, saying bin Laden apparently "hadn't even prepared a defense" and had "no intention of fighting."

According to an earlier and contradictory account from a U.S. official, bin Laden was shot after the SEALs went into the room. That account said the al Qaeda leader was moving, possibly toward one of the weapons that were in the room when he was shot. He never had a gun in hand but posed an imminent threat, according to the U.S. official.

Bissonnette said he had mixed feelings about President Barack Obama, who ordered the operation.

"None of us were huge fans of Obama. We respected him as the commander-in-chief of the military and for giving us the green light on the mission," wrote the former SEAL, who was a 36-year-old chief petty officer when he left the Navy as a highly decorated commando in April.

CNN obtained a copy of the book, which will officially be released September 4. It first had a release date of September 11, but Dutton, a Penguin imprint, said the book will come out early because of "overwhelming excitement in the marketplace."

The first printing of the book, already an Amazon best seller, is now 575,000 copies, according to Dutton.