"(We) trained our lasers on his chest and fired several rounds. The bullets tore into him, slamming his body into the floor until he was motionless," Owen writes according to a copy of the book obtained by the Huffington Post.
The SEALs later found two weapons stored by the doorway, untouched, the author said. Neither weapon was loaded.
"He hadn’t even prepared a defense. He had no intention of fighting. He asked his followers for decades to wear suicide vests or fly planes into buildings, but didn’t even pick up his weapon," Owen writes.
Bin Laden was apparently wearing a white t-shirt, loose tan trousers and a tunic.
The account in No Easy Day contradicts the official version of events, which stated that bin Laden was shot only after he returned to his bedroom because they assumed he was searching for a weapon.
White House spokesman Tommy Vietor would not comment on the apparent contradiction late on Tuesday.
No Easy Day was due out Sep 11, but Dutton announced the book would be available a week early, on Sep 4, because of a surge of orders due to advance publicity that drove the book to the top of the Amazon.com bestseller list.
In another possibly uncomfortable revelation for US officials who say bin Laden’s body was treated with dignity before being given a full Muslim burial at sea, the author reveals that in the cramped helicopter flight out of the compound, one of the SEALs called “Walt” was sitting on bin Laden’s chest as the body lay at the author’s feet in the middle of the cabin.
The publisher says the author used pseudonyms for all the SEALs.
Owen also writes disparagingly that none of the SEALs were fans of President Barack Obama and knew that his administration would take credit for ordering the May 2011 raid. One of the SEALs said after the mission that they had just secured re-election for Obama by carrying out the raid.
But he says they respected him as commander in chief and for giving the operation the go-ahead.
Owen writes less flatteringly of meeting Vice President Joe Biden along with Obama at the headquarters of the 160th Special Operations Aviation Regiment after the raid. He says Biden told “lame jokes” no one understood, reminding him of “someone’s drunken uncle at Christmas dinner”.
Beyond such embarrassing observations, US officials fear the book may include classified information, as it did not undergo the formal review required by the Pentagon for works published by former or current Defense Department employees.
Officials from the Pentagon and the CIA, which commanded the mission, are examining the manuscript for possible disclosure of classified information and could take legal action against the author.
In a statement provided to The Associated Press, the author says he did “not disclose confidential or sensitive information that would compromise national security in any way”.
Owen’s real name was first revealed by Fox News, but publishers Dutton Penguin requested it to be withheld. Jihadists on al-Qaeda websites have posted purported photos of the author, calling for his murder.
