The man who gunned down a US CEO in New York City was still at large on Thursday as authorities raced to find him.

The New York Police Department (NYPD) released new photos of the suspect and urged people to come forward if they have information.

On Wednesday, UnitedHealthcare CEO Brian Thompson was shot and killed as he walked to his company's annual investor conference at the Hilton Hotel in Midtown, Manhattan. 

The shooting took place just blocks away from major tourist sites in the city and Thompson appeared to be directly targeted.

US media reported that authorities found words written on the casings of the bullets used.

Suspect used gun silencer

NYPD chief of detectives Joseph Kenny said the shooter wore a black face mask, black-and-white sneakers and carried a distinctive gray backpack.

The gunman arrived outside the hotel some five minutes before Thompson did. He waited and then approached Thompson from behind, firing his 9mm pistol.

Kenny said that the man knew how to handle firearms, as the gun jammed but he quickly fixed it and kept firing.

"From watching the video, it does seem that he's proficient in the use of firearms as he was able to clear the malfunctions pretty quickly," Kenny said.

New York Mayor Eric Adams said on Thursday that the suspect had used a silencer gun to shoot Thompson.

"In all of my years in law enforcement, I have never seen a silencer before," Adams, a retired NYPD captain, told US broadcaster MSNBC.

"And so that was really something that was shocking to us all," he added.

The shooter fled on a bicycle and was last seen riding into Central Park. Police released several surveillance images of the man wearing a hooded jacket and a mask covering most of his face.

The hunt for the gunman has taken New York City police to at least two hostels on Manhattan's Upper West Side, following a tip that the suspected shooter may have stayed at one of the residences.

Investigators now believe the suspect may have traveled to New York last month on a bus that originated in Atlanta, one of the law enforcement officials said.

Words found on bullet casings

The motive remains unknown, but US media reported that the words "deny," "defend," and "depose," were found on three bullet casings used in the shooting.

According to US broadcaster NBC News, the words may be linked to the title of a 2010 book about US insurance companies called "Delay Deny Defend," whose subtitle is "Why Insurance Companies Don't Pay Claims and What You Can Do About It."

A US Senate panel had been investigating UnitedHealthcare's history of insurance claim denials.

In particular, the panel was investigating how UnitedHealthcare and other companies deny care to patients who are enrolled in Medicare Advantage plans, which is a private version of Medicare that covers millions of older Americans.

The panel was also investigating the use of artificial intelligence to deny those claims.

According to the Senate's Permanent Subcommittee's report released earlier this year, UnitedHealthcare denied nearly a quarter of claims, a rate that doubled over just a two-year period from 2020 to 2022.

jcg/ab (AP, Reuters)