UnitedHealthcare CEO Brian Thompson may have been assassinated with a rare World War Two era-inspired gun.
The 50-year-old was shot to death on Wednesday as he made his way to an investor conference at the New York Hilton Midtown Manhattan hotel.
His assailant was a masked gunman who opened fire from behind and struck Thompson in the back and leg.
Police are yet to recover the murder weapon, however police sources told the New York Post the gun is thought to be a Swiss-made Brugger & Thomet VP9.
The rare firearm is an update to the British World War Two era Welrod pistol and is typically used for putting down large animals such as horses.
The Welrod has an inbuilt suppressor, which made it perfect for sneaking up and executing enemies.
The B&T VP9 has a similar inbuilt silencer designed to muffle the sound of a gunshot and avoid panicking the animal being executed or other animals nearby.
A halal cart owner on the street where the assassination took place told DailyMail.com he did not hear anything, despite being open at the time of the killing.
Guests at the nearby Hilton, some of whose rooms overlooked the same street, also told of their shock at waking up to the news of the slaying, having slept soundly throughout.
The VP9's latest version holds standard 9mm rounds, features a three inch barrel and weighs just over two pounds. It retails for around $2,000.
'This updated, integrally suppressed pistol features a new grip and updated magazines, yet maintains its non-descript appearance, whisper-quiet sound signature and unique rotating bolt operation,' the manufacturer states on its website.
Cops were said to be eying the sale of a firearm in Connecticut which could match up with the theory, per the Post however this proved to be a red herring.
Surveillance footage of the cold-blood killing showed the assassin walk up and shoot Thompson in the back before the gun appeared to jam.
He quickly resolved the issue and carried on firing as the CEO crumpled to the floor.
'It could be [the gun used] but it is not common and by no means what I first thought about,' former FBI agent Robert D'Amico told DailyMail.com.
'But with that said, the fact he had a "malfunction" and recognized it immediately and manually fed a new round in could indicate in fact it was a gun like this that can only function manually.'
Investigators found bullet casings at the scene which were inscribed with the words, 'deny,' 'depose' and 'defend'.
The words bear similarity to the 2010 book by Professor Jay M. Feinman, Delay, Deny, Defend: Why Insurance Companies Don't Pay Claim and What You Can Do About.
As of Friday afternoon, the killer remains at large with a frantic manhunt unfolding across the country.
