The U.S. Department of Justice is investigating a former Navy SEAL who helped kill Osama bin Laden and later wrote a book about the operation, The New York Times reported. Matt Bissonnette, who penned "No Easy Day" under the pseudonym Mark Owen, may have revealed classified material, federal officials say.

The alleged disclosures may not be related to the book, which reportedly yielded Bissonnette millions of dollars in royalties, but rather the author's engagements upon the book's release.

"People familiar with the inquiry said investigators seemed more interested in paid speeches (he) ... gave at corporate events," the newspaper wrote.

In one such event in Atlanta, audience members were allegedly asked to turn in their cell phones so Bissonnette's speech could not be recorded.

The department's investigation could result in criminal charges for the former SEAL, according to The Associated Press. The recent inquiry evolved from an inquiry the Pentagon launched when it learned of Bissonnette's book, which was published without a (potentially required) review by defense officials.

Bissonnette was a member of the Navy's SEAL Team 6, which is believed to be the unit involved in the May 2, 2011, "Operation Neptune Spear" that killed Bin Laden. The longtime leader of the terrorist group al-Qaida had been hiding in a compound in the Pakistani city of Abbottabad.

Bissonnette's lawyer, Robert Luskin, told The New York Times that the Justice Department ultimately rejected a proposed agreement that would have forced Bissonnette to hand over a part of the royalties he earned for "No Easy Day." It would have also shielded the author from criminal charges.

In the meantime, Bissonnette has completed a sequel to the book, titled "No Hero: The Evolution of a Navy SEAL," which will be released Nov. 10. This time, the author submitted the tome for Pentagon approval, according to his lawyer.

A number of fellow members of the military have criticized the former SEAL for violating the cloak of secrecy that typically surrounds the units' operations.

Jerry Hendrix, a retired Navy captain and a senior fellow at the Center for a New American Security, said that in a book such as Bissonnette's, "whether you mean to or not, you're going to reveal tactics, techniques and procedures."