This combination of images provided by the New York City Police Department shows the suspect sought in the killing of UnitedHealthcare CEO Brian Thompson outside a Manhattan hotel where the health insurer was holding an investor conference, Wednesday, Dec. 4, 2024. (New York City Police Department via AP)

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The masked gunman who killed the leader of one of the largest U.S. health insurance companies in front of midtown Manhattan surveillance cameras remained free Thursday from the dragnet thrown by the nation’s largest police department.

UnitedHealthcare CEO Brian Thompson, 50, died in the dawn ambush Wednesday. Thompson was walking to the company’s annual investor conference at a Hilton in Midtown, blocks from tourist draws like Radio City Music Hall and the Museum of Modern Art.

On Thursday, a law enforcement official said the shooter had used ammunition with the words “deny,” “defend” and “depose” written on it. The official was not authorized to publicly discuss details of the ongoing investigation and spoke to the Associated Press on the condition of anonymity.

The words on the ammunition may have been a reference to strategies insurance companies use to try to avoid paying claims.

This image provided by the New York City Police Department shows a man wanted for questioning in connection to the investigation of the killing of UnitedHealthcare CEO Brian Thompson outside a Manhattan hotel, Wednesday, Dec. 4, 2024. (New York City Police Department via AP)

What happened?

Police said Thompson was heading to the company's annual investor conference at the New York Hilton Midtown around 6:45 a.m. when a person walked up behind him and shot him.

Thompson was alone and did not have bodyguards, police said.

Officers found Thompson on the ground with gunshot wounds to his back and right calf, according to Joseph Kenny, the NYPD chief of detectives. The CEO was pronounced dead at a nearby hospital at 7:12 a.m.

What do we know about the shooter?

Kenny said the shooter wore a black face mask, black-and-white sneakers and a distinctive gray backpack.

He arrived outside the hotel about five minutes before Thompson did, then waited and ignored other pedestrians before he approached Thompson from behind.

After the assailant began to fire, his 9 mm pistol jammed but he quickly fixed it and kept firing, Kenny said, another sign of the shooter's professionalism.

“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.

The shooter ran into an alleyway near the hotel and later got on the e-bike that he took into Central Park.

Police initially said the shooter rode into Central Park on a bicycle from the city’s bike-share program, CitiBike. But a spokesperson for the program’s operator, Lyft, said police officials informed the company Wednesday afternoon that the bike was not from the CitiBike fleet.

Kenny said police found a cellphone in the alleyway, but it was unclear if it belonged to the shooter.

Members of the New York police crime scene unit pick up cups marking the spots where bullets lie as they investigate the scene outside the Hilton Hotel in midtown Manhattan where Brian Thompson, the CEO of UnitedHealthcare, was fatally shot Wednesday, Dec. 4, 2024, in New York. (AP Photo/Stefan Jeremiah)

Who was Brian Thompson?

Thompson was the chief executive of UnitedHealthcare, the insurance wing of parent company UnitedHealth Group Inc.

He had worked at the Minnetonka, Minnesota-based company for two decades and led its insurance division since 2021. He was one of the company's highest-paid executives, with a $10.2 million annual compensation package.

Thompson kept a low profile, with UnitedHealth Group Inc.'s CEO Andrew Witty taking on a more public-facing role that included testifying before Congress.

This undated photo provided by UnitedHealth Group shows UnitedHealthcare chief executive officer Brian Thompson. (AP Photo/UnitedHealth Group via AP)

Thompson, as earlier reported by The Des Moines Register, grew up in Iowa and graduated in 1993 from South Hamilton High School in Jewell, located in central Iowa.

In a statement Wednesday, the South Hamilton school district said Thompson was the valedictorian of the 1993 class. “During his time at South Hamilton, Brian was a star student, athlete, homecoming king and respected leader,” the school district said. “His achievements and character left a meaningful legacy within our schools and community.”

After high school, Thompson attended the University of Iowa from 1993 to 1997, earning a bachelor’s of business administration and accounting. Among many honors and scholarships, he reported in his LinkedIn profile attaining the highest cumulative scholastic grade-point average at UI in 1997, making him valedictorian and the Delta Sigma Pi Scholarship key recipient.

He lived in the Minneapolis suburb of Maple Grove and was the married father of two sons in high school.

His wife, Paulette Thompson, told NBC News that her husband said some people had been threatening him. She did not have details, but suggested they may have involved issues with insurance coverage.

Maple Grove Police Chief Eric Werner said his department had not received any reports of threats against the executive.