New York authorities have released images of the suspected of the daylight assassination of a health insurance boss on a Manhattan street.

In other developments, police found a backpack they believe belong to the gunman, while New York City Mayor Eric Adams said the man had been identified

“The net is tightening,” Adams told reporters at a Police Athletic League holiday party in Harlem, was quoted as saying on Saturday (US time) by the New York Post.

He declined to name the suspect.

Thompson, 50, who became CEO of UnitedHealth’s insurance unit in April 2021, was shot in the back early on Wednesday in what police described as a targeted attack by a masked assailant lying in wait.

The murder occurred just before the company’s annual investor conference at the Hilton hotel on Sixth Avenue.

The shooting sparked a massive manhunt for the gunman, who fled on foot wearing a hooded jacket, balaclava and gray backpack before mounting an electric bike and riding into Central Park, police said.

Adams was quoted by the Post as saying the police were withholding the suspect’s name for now to deny him any advantage.

“We don’t want to release that now,” the mayor said.

“If you do, you are basically giving a tip to the person we are seeking and we do not want to give him an upper hand at all. Let him continue to believe he can hide behind the mask.”

“We revealed his face,” he continued, referring to security camera photos and video released after the murder.

“We’re going to reveal who he is and we’re going to bring him to justice.”

On Sunday, police released new photographs of the wanted man. They show him masked with a hood in the backseat of a vehicle and wearing a jacket walking on the street.

Elsewhere, there were media reports on Sunday that a Peak Design backpack resembling the one worn by the suspect had been recovered near a playground in Central Park.

MSNBC said on Saturday that police examining the bag and its contents found a jacket and Monopoly money, but no firearm.

There is also no sign of the e-bike the suspect used to flee the scene of the shooting.

Other evidence gathered since last Wednesday’s deadly attack includes DNA and a partial fingerprint from a discarded Starbucks water bottle, a discarded “burner” mobile phone and nine-millimetre shell casings with the words “delay,” “deny” and “depose” written on them.

Police have offered a reward of up to $US10,000 ($A15,600) for information about the shooter. The FBI said it would also offer a reward, of up to $50,000, for information “leading to the arrest and conviction of the individual responsible for this crime”.

New York police said on Friday they believed the suspect had left New York City, after video emerged showing him climbing into a taxi that took him to a bus station.

The circumstances of the attack suggested it was premeditated and planned, police said. Video shows the suspect ignoring other pedestrians while appearing to wait for Thompson.

Security video showed him behind Thompson, raising his handgun and firing at his back. Thompson, a married father of two, suffered gunshot wounds to his back and leg and was pronounced dead at a hospital shortly after the attack.

UnitedHealth is US’s largest health insurer, providing benefits to tens of millions of Americans, who pay more for healthcare than people in any other country.

-with AAP