WARNING: Graphic content.

Ever since Osama bin Laden was killed by US special forces during a raid on his hide-out in Pakistan, photos of the September 11 mastermind’s dead body have been kept a closely guarded secret by the US government.

Now it seems at least one special forces operative has kept a memento.

The man who shot bin Laden dead during the dramatic May 2011 raid, Matthew Bissonnette, has given a hard drive containing the picture to authorities as part of a deal to escape being charged, according to US website The Intercept.

Mr Bissonnette, a former member of Navy SEAL Team Six that carried out the infamous kill mission, was under investigation for unlawfully possessing classified information after penning a book about the terror leader’s death.

But the inquiry into Mr Bissonnette reportedly widened after he handed over the hard drive and the picture of bin Laden’s corpse was discovered on it.

After bin Laden’s special ops killing, Mr Bissonnette wrote the 2012 book No Easy Day, which was his account of the plan to kill the al-Qaeda leader as he hid in a compound in the outskirts of the Pakistani city of Abbottabad, surrounded by bodyguards.

The highly controversial book shot straight to the top of the bestseller list but landed Mr Bissonette in trouble for breaking an “unwritten code of silence” among special ops soldiers with all the sensitive information it contained.

He later admitted he had also broken military rules by not allowing the Department of Defense to review the book’s manuscript, triggering several Navy inquiries.

After his death, the US said bin Laden’s body was dumped at sea at an undisclosed location because of security concerns. The corpse was taken to the mystery spot on an aircraft carrier.

Few details about what happened to bin Laden’s body have been revealed. According toThe Independent an email stamped secret and sent on May 2, 2011 by a senior Navy officer described how bin Laden’s body was washed, wrapped in a white sheet, and then placed in a weighted bag.

The heavily redacted emails, obtained under freedom of information laws, suggest few people actually witnessed the body being dumped in the sea.

But actual images of the disposal have been kept away from the public and the media.

One person who has seen them is the US President Barack Obama. He told CBS there were good reasons why they were being withheld.

“Keep in mind that we are absolutely certain this was him. We’ve done DNA sampling and testing. And so there is no doubt that we killed Osama bin Laden,” the President said.

“It is important for us to make sure that very graphic photos of somebody who was shot in the head are not floating around as an incitement to additional violence. As a propaganda tool.”

One estimate was that as few as 50 people had seen the images. One of those, Republican Senator James Inhofe, has described in detail what he saw.

“One of the shots went through the ear and out through an eye socket, or through the eye socket and out through the ear and exploded, that was the kind of ordinance it was. That caused the brains to be hanging out of the eye socket,” he told CNN.

Inhofe was sure it was bin Laden. “Absolutely no question about it. A lot of people out there say: ‘I want to see the pictures,’ but I’ve already seen them. That was him. He’s gone. He’s history.”

The secrecy has fuelled speculation that the US is hiding something about the mission and bin Laden’s death, leading to countless conspiracy theories.

These even included the suggestion bin Laden is still alive — that he had somehow escaped and the Americans were so embarrassed they came up with a cover story that he had been killed.

Another theory is that bin Laden is in fact dead, but died long before 2011 and it suited the US to keep hunting for him to justify their fight against the Taliban in Afghanistan.

Another popular theory is that bin Laden is being sheltered, under house arrest, by the Pakistani government, which is hiding him from the US.

Many people find it unbelievable the most wanted man in the world could have been living undetected in Pakistan for as long as he did.

Mr Bissonnette’s lawyer, Robert Luskin, wouldn’t confirm to CNN if his client had an image of bin Laden or comment on the specifics of The Intercept report.

But he did reveal the investigation into his client was now over.

“I can confirm that the criminal investigation of Mr Bissonnette for alleged wrongful handling or disclosure of classified information was closed through declination by the [Department of Justice] in August 2015,” said Mr Luskin.

He revealed a deal he’d brokered between Mr Bissonnette and the US Government involved his client giving a portion of the money he’d earned in book sales

He said that he had negotiated a deal in 2014 with the Pentagon and the Justice Department to hand over to the government some of the millions of dollars in book profits Mr Bissonnette had received for the book.

The book was a massive change from the usual secrecy surrounding US military operations and was written under a pen name.