New York, New York - New York police scoured the city Thursday for a masked gunman who shot a top health insurance executive at close range in a brazen daylight killing outside a Manhattan hotel.

In a hit conducted in front of bystanders and seen by millions on TV replays of security camera footage, the killer used a pistol to gun down Brian Thompson, CEO of UnitedHealthcare – one of the country's largest medical insurers.

Thompson was attending an investor conference in the Midtown business district.

Police have yet to suggest a motive and would not confirm a New York Times report that the words "delay" and "deny" – often used by insurance companies to reject claims – were written on shell casings found at the scene.

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Video footage shows Thompson on the sidewalk outside the New York Hilton Midtown when an unidentified hooded suspect approaches from behind with a handgun and fires several shots at his 50-year-old victim, who crumples on the ground.

Camera footage showed the suspect then fleeing on foot, before getting on a bicycle – which police initially said may have been a rented e-bike. Police said he went in the direction of Central Park.

"Every indication is that this was a premeditated, preplanned, targeted attack," New York's police Commissioner Jessica Tisch told a briefing Wednesday.

NYPD chief of detectives Joseph Kenny would not confirm reports that a silencer was used on the pistol, saying that the question would be part of the investigation, but he did confirm that a cell phone had been recovered from the scene.

In the absence of an arrest, speculation has been rife that the gunman may have sought to take revenge for adverse medical coverage decisions made by the insurer.

Minnesota-based Thompson's wife Paulette Thompson told the NBC News outlet that he had received unspecified threats.

"There had been some threats basically, I don't know – [over] a lack of coverage? I don't know details," said Paulette Thompson, who had two children with her late husband.

In a statement, UnitedHealth Group – the parent company of UHC – said it was "deeply saddened and shocked."

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UnitedHealthcare is a major player in the lucrative US health care market, providing workplace insurance, as well as administering huge health care programs like Medicare and Medicaid for older and low-income people funded by state budgets.

Police remained on the scene of the killing, and have been combing through Manhattan's iconic Central Park with dogs and drones.

"We have a large detective agency. At any given hour, multiple detectives could be working on (the investigation)," a spokesman for the NYPD said. "We will be using all our assets that we have."

The spokesman said that no follow-up briefing had been planned.

UnitedHealth Group had revenues of $100.8 billion in the third quarter of the year. Thompson's own compensation package in 2023 was $10.2 million, according to a regulatory filing.

He had been chief executive of UnitedHealthcare since April 2021, according to a separate Securities and Exchange Commission filing.

Before that, he oversaw UnitedHealthcare's government programs, including Medicare, from July 2019 to April 2021.