NEW YORK, Dec 6 (Reuters) - Armed with a growing file of

clues, New York police on Friday were scouring surveillance

videos and asking the public for help in their search for the

masked assailant who gunned down a UnitedHealth ( UNH )

executive on a Midtown Manhattan sidewalk.

Brian Thompson, 50, the CEO of UnitedHealth's ( UNH ) insurance unit

and a father of two, was shot from behind early on Wednesday in

what police described as a brazen and targeted attack. It came

just before the company's annual investor conference at the

Hilton on Sixth Avenue.

Police have released multiple photos of the suspect that

were captured by security cameras from around town during his

stay in New York. They have yet to publicly identify the man,

who was last seen riding an electric bicycle into Central Park.

Police offered a $10,000 reward for information leading to

an arrest and conviction.

The words "deny," "defend" and "depose" were carved into

shell casings found at the scene, police sources told ABC and

the New York Post. A New York City Police Department

spokesperson would not comment on the report.

The words evoke the title of author Jay Feinman's 2010 book

critical of the insurance industry entitled "Delay Deny Defend:

Why Insurance Companies Don't Pay Claims and What You Can Do

About It." Feinman, a professor emeritus at Rutgers University

Law School, declined to comment.

UnitedHealth ( UNH ) is the largest U.S. health insurer, providing

benefits to tens of millions of Americans, who pay more for

healthcare than people in any other country. Thompson joined

UnitedHealth ( UNH ) in 2004 and became the CEO of UnitedHealthcare, a

unit of UnitedHealth Group ( UNH ), in April 2021.

Investigators believe the suspect arrived in New York City

on Nov. 24 after traveling from Atlanta by bus, CNN reported,

citing unnamed law enforcement sources. The suspect checked into

a hostel in the city with a fake identification and paid with

cash, CNN reported.

Detectives believe the perpetrator was experienced with

firearms based on how he slowly and deliberately carried out the

shooting, CNN reported, citing police sources who spoke on the

condition of anonymity because the investigation was ongoing.

Security video showed the shooter, wearing a hooded

sweatshirt, ski mask and a gray backpack, walking up behind

Thompson, raising his handgun and firing at his back. Police

said the gunman arrived outside the hotel several minutes before

Thompson and waited for him to walk past before firing, ignoring

other passers-by.

CNN, whose reporter John Miller is a former NYPD deputy

commissioner, said police found a phone in an alley that the

gunman ran through and also recovered a water bottle the shooter

bought just minutes before the attack.

A fingerprint on the water bottle was too smudged to provide

further clues about the shooter, the New York Times reported,

citing a senior law enforcement official.

New York has one of the most advanced surveillance systems

of any major U.S. city, largely built after the attacks of Sept.

11, 2001, said Felipe Rodriguez, a former NYPD detective

sergeant who is now an adjunct professor at John Jay College of

Criminal Justice in New York.

There are thousands of cameras in New York and all feeds can

be monitored in real time as well as reviewed for previous

video, aided by facial recognition software.