BRIAN Thompson could have been assassinated with a rare WW2-inspired spy gun that had bullets with a secret message on them.
The UnitedHealthcare boss was assassinated in a brazen execution in Midtown Manhattan on Wednesday in a chilling act caught on CCTV.
The gun used by the shooter appears to match a Brugger & Thomet VP9 - a Swiss gun that is known for its use by vets to put down large sick animals, like a horse, sources told the .
The inspiration for the firearm comes from a Welrod pistol - a British gun developed by special forces in WW2.
Its mechanical design and inbuilt suppressor meant the Welrod is quiet - so the shooter could assassinate Nazis.
The B&T VP9 shares an almost identical design, but is meant to be quiet so as not to scare other animals.
Read more on US news
The '9' in the gun's name refers to its 9mm bullets - matching the size of the ammunition cops found at the scene outside the Hilton Hotel.
The shooter wrote in pen on the bullets the words “deny,” “depose” and “defend”.
The words could be a reference to a book published in 2010 by insurance law expert Professor Jay M. Feinman titled: Delay, Deny, Defend: Why Insurance Companies Don't Pay Claim and What You Can Do About.
The book is boldly critical of the insurance industry and accuses companies of developing "unethical practices of delaying or denying legitimate claims."
Most read in The US Sun
A description of the book states that it contains "dozens of stories involving major insurers" and aims to counsel readers "on how to make insurance buying decisions and pursue disputed claims."
The book's author, Jay M. Feinman, refused to speak following the murder.
The phrase is also commonly used by lawyers and insurance critics to describe tactics used to avoid paying claims.
It refers to insurers delaying payment, denying a claim and then defending their actions.
Health insurers like UnitedHealthcare have become frequent targets of criticism from doctors and patients for denying claims or complicating access to care.
There is speculation the killer could have been a disgruntled patient with UnitedHealthcare exacting some form of revenge.
A $10,000 reward for information related to the shooter leading to their arrest has been offered by the NYPD.
Cops have also released a new CCTV snap of the suspected killer smiling as he flirts with a staff member at the hostel he stayed at.
The suspect, who had been masked in all other images released, slipped up and pulled down the covering to reveal his face.
Cops tracked him to the hostel after they found other CCTV footage of him in the area at 5am on Wednesday - just an hour before he's believed to have shot the UnitedHealthcare CEO.
The NYPD and FBI are desperately hunting for the suspect after he fled the killing into Central Park and then disappeared.
He arrived in the city on a Greyhound bus that travelled from Atlanta to New York, but authorities don't know when he boarded it.
Mystery surrounds the assassination of the healthcare CEO, with expert former senior British military intelligence officer Phillip Ingram claiming it was a professional hit.
Speaking exclusively to The Sun, Ingram revealed the three clues that suggest the hooded shooter was a pro.
He said: "It's very clear that this was a professional assassination.
"Because the way an individual, came into profile in the CCTV pictures that we've seen, having let his victim walk past him and then pull a gun out with a rather large silencer on it and fire a number of rounds.
"We saw the gun jamming, and he cleared the jam very professionally, killing his victim as he wanted to do, and then moved off, but in a way that he hid his identity.
"He had clearly checked the area out for where the CCTV coverage was beforehand. And what's interesting is there are reports to say that there are words on some of the shell cartridges that have been found by the police. So there was a clear message being sent.
"So this was very professionally put together. The individual was aware of how to handle a weapon.
"This was someone who knew what he was doing. And in the nerves of the moment and using a weapon with a silencer.
"First round hit his victim in the calf. Second round hit him in the chest, which is where you'd be aiming for."
TRIBUTES PAID
Meanwhile, Thompson's wife, Paulette, said her husband had been receiving threats in the run-up to his murder.
A fake bomb threat targeting Thompson's home was sent approximately 12 hours after his assassination, as reported by .
It has also been revealed the couple were estranged, with the pair living in separate homes less than a mile apart in suburban Maple Grove, Minnesota.
An emotional Paulette paid tribute to her late husband in a statement.
"Brian was an incredibly loving, generous, talented man who truly lived life to the fullest and touched so many lives," she said.
"Most importantly, Brian was an incredibly loving father to our two sons and will be greatly missed."
READ MORE SUN STORIES
Thompson, who had been the CEO of America's largest private health insurer since April 2021, earned a salary of almost $9.9 million.
He was with the company for 20 years and was reportedly under investigation by the Department of Justice at the time of his death.
Timeline of Brian Thompson's murder
BRIAN Thompson, the 50-year-old CEO of UnitedHealthcare, has been shot to death, and a desperate search is underway for his killer.
Here is everything we know about Thompson's murder so far.
December 2 - Thompson travels from his home in Minnesota to New York City for an investor conference in Midtown Manhattan.
December 4, 6:45 am - Thompson walks from his hotel across the street to the New York Hilton Midtown and is murdered by a masked shooter. The execution was caught on surveillance, and the suspect was seen biking away toward Central Park. Cops spark a citywide search for the assassin.
December 4, later that morning - News broke the shooting victim was Thompson, who was the CEO of America's largest private healthcare provider. Cops released disturbing images of the execution, offered a reward for information, and made a desperate plea for New Yorkers to keep their eyes out.
December 4, afternoon - Thompson's estranged wife Paulette revealed her husband had been threatened before he was shot.
December 4, afternoon - Cops released more eerie images of the suspect ordering at Starbucks that partially revealed his face. The U.S. Sun confirmed the coffee shop was just two blocks away from the shooting, but it's unclear when he stopped by.
December 5, morning - Reports claim the words "deny," "dispose," and "defend" were engraved on live rounds and shell casings left behind by the assassin. These words echo the book Delay, Deny, Defend, which is about the failings of the healthcare industry. The author of the book had no comment on the reports.
December 5, morning - Cops raid a hostel in the Upper West Side of New York City where the suspect is said to have stayed. It's believed he wore a mask for most of the time he was there.
December 5, morning - A person of interest in Thompson's murder is pictured. He's wearing a hood in the photo, but his full face could be seen breaking into a beaming grin. Still, no arrests have been made in the investigation.