It has all the hallmarks of a dramatic spy movie.

At around 6.45am on Wednesday, a masked assassin shot dead a multi-millionaire executive on one of New York’s busiest shopping streets.

After confirming he’d eliminated his target, the hooded gunman walked calmly away, before apparently disappearing into thin air in one the world’s most surveilled cities.

His victim: UnitedHealthcare CEO Brian Thompson, 50, who earned $10 million a year, suffered at least two gunshot wounds – one to the back, the other in his leg – outside the Hilton Hotel on Manhattan’s Sixth Avenue. He was later pronounced dead in hospital.

It appears to have been a targeted attack, police say, with the assassin lying in wait outside the Hilton for about five minutes before Thompson emerged from his hotel over the street.

The executive had arrived in the city on Monday and was making his way to his company’s annual investor conference, due to be held in the Hilton and at which he was expected to announce bumper predicted revenues of over $450 billion. UnitedHealthcare is the largest health insurance provider in the US.

Chilling CCTV footage shows the assassin stepping out from behind a vehicle and shooting Thompson – who didn’t see his killer coming – with a large handgun that appears to have been fitted with a silencer. The first bullet sends Thompson, a married father-of-two, stumbling to the floor while a mystery bystander flees.

The killer’s gun then appears to jam, prompting him to adjust the weapon, before stepping closer to Thompson and taking another shot.

Police were called promptly but the killer, carrying a distinctive grey backpack, had already fled the scene on foot.

Dashing through an alleyway, he then got onto what is thought to have been an electric bike, before cycling up Sixth Avenue and into Central Park. He’d vanished by 6.48am – just three minutes after the shooting. There has been no sign of him since.

Despite a frantic manhunt, the offer of a $10,000 reward for information, and all of New York City’s policing might, worryingly little is known about who Thompson’s killer is, his motive, and where he is now…

Here, the Daily Mail details the key questions that remain unanswered:

Who is the shooter?

Images from surveillance footage show the shooter to be a light-skinned man wearing a dark hooded jacket, a black face mask, black and white sneakers, and carrying a large grey backpack.

Police do not yet know, or at least have not released, his identity. They say it seems unlikely that he and Thompson had crossed paths before.

The attack does, however, seem to have been premeditated.

‘He appeared to wait for his intended target,’ New York Police Department commissioner Jessica Tisch said Wednesday. ‘I want to be clear: At this time, every indication is that this was a premeditated, preplanned, targeted attack.’

Of particular concern is how confidently the gunman appeared to handle his weapon. Indeed, he quickly overcome an apparent jam in the midst of the shooting. There has been speculation that he could be a trained killer or is at least experienced with firearms.

The type of gun he used is also important; it was a handgun with what appeared to be a silencer attached. It is illegal to buy or use a silencer in the state of New York.

Who is the mystery woman?

Footage of the attack shows a figure, who appears to be a woman dressed in dark clothing and holding a coffee cup, fleeing from a doorway as the assassin opens fire just meters away.

We do not yet know who this person is, but there has been no suggestion that they were involved or knew Thompson.

Indeed, they appeared to be surprised by the shooting, cowering in a doorway when the first shot rang out, before making a run for it.

Police will no doubt be desperate to identify this key witness.

What’s on the discarded phone – and where is the shooter’s bike?

Police say they recovered a phone from the alley down which the shooter fled. They have not yet revealed what is on the phone, or confirmed that it even belonged to the shooter – but they do say they are performing forensic analysis on it.

It is understood that the shooter fled on foot to Sixth Avenue where he picked up an electric bike and rode up to Central Park, entering on Center Drive before disappearing.

Police initially said they were working with Lyft, the taxi company that owns Citi Bike, to track one of their e-bikes – which are all fitted with GPS. However, on Wednesday night, a law enforcement official told CNN that information was incorrect, claiming that the e-bike the shooter used was not a Citi Bike.

It is not yet clear how the bike was obtained. Rentable e-bikes have to be paid for and users must have memberships – which would mean electronically stored details. The bike could, of course, have been stolen or someone else’s membership details could have been used. It might also have been privately procured by the shooter.

What was in the backpack?

Despite a massive ongoing manhunt with drones, dog units, helicopters and officers on the ground, police seem no closer to finding the shooter.

His last known location was entering Central Park at 6.48am.

Given the large backpack he was carrying, he may well have had a change of clothes that allowed him to slip out of the park unnoticed.

The atmosphere in the park on Wednesday afternoon was described by journalists as normal despite the grim news, with runners and walkers going about their usual business.

Police have had more luck tracking the assassin’s movements before the shooting, with news images from CCTV footage surfacing Wednesday afternoon of him in a Starbucks nearby to the Hilton Hotel and minutes before the attack.

It is not yet clear whether he ordered anything to eat or drink. In the images he appears to be holding a small object in his hands. One senior police official reportedly told CNN that the footage shows the gunman purchasing two power bars and a bottle of water.

Police are clearly confident that the gunman has fled the immediate area, as the annual Christmas tree lighting at the iconic Rockefeller Center – just blocks away – was allowed to go ahead on Wednesday evening. Thousands of New Yorkers and tourists attend each year.

What was the motive?

An official motive for the shooting has not yet been released, but there is widespread speculation online that the attack was linked to Thompson’s job – as the head of a controversial health insurance company.

Thompson’s 51-year-old wife, Paulette – with whom he lived in a $1.5 million home in Minnesota – told NBC that her husband had been receiving threats in the days before the shooting.

‘There had been some threats… Basically, I don’t know, a lack of [insurance] coverage?’ she said, ‘I don’t know details. I just know that he said there were some people that had been threatening him.’

‘I can’t really give a thoughtful response right now,’ she added, ‘I just found this out and I’m trying to console my children.’

The couple share two sons.

Despite having such a high-profile job, Thompson seems to have kept a low profile and was known by few outside the industry.

He was named as CEO in 2021, leading United’s division that deals with Medicare and Medicaid, overseeing the health coverage of more than 49 million Americans, and helping to bring in $281 billion in revenue for the company in 2023.

The Department of Justice launched an investigation into the company last year, probing whether the insurer was unfairly restricting competitors and running a monopoly.

In May this year, Thompson and other executives were subsequently sued for alleged fraud and insider trading. A complaint lodged by a pension fund claimed Thompson had failed to tell investors about the DoJ probe before unloading 31 percent of his personal company shares, taking $15.1 million in profit.

The complaint alleges that Thompson and other execs collectively sold over $100 million in company stock during the four-month period when insiders knew about the federal investigation, but the public did not.

In February this year, United was hit by one of the largest healthcare data breaches in US history, with the company estimating that as many as one-third of Americans’ private data — potentially including Social Security numbers — had been compromised.