Police are closing in on the suspect in the murder of UnitedHealthcare CEO Brian Thompson outside a New York hotel, the city’s mayor has said.

New York Mayor Eric Adams said on Sunday that the “net is tightening” around the suspected gunman, who is believed by authorities to have left the city after the killing.

“The manner in which they were able to follow his footsteps, to recover evidence – some of it is known, some of it is unknown – but the net is tightening. And we are going to bring this person to justice,” Adams told reporters.

Asked if authorities had confirmed the suspect’s name, Adams declined to comment on his identity.

“We do not want to give him an upper hand at all. Let him continue to believe he can hide behind a mask,” he said.

The New York Police Department (NYPD) has released several images of the suspect, including CCTV stills of the man at a hostel with his face partially visible.

Thompson, 50, was shot dead on Wednesday in an early morning ambush outside the New York Hilton Midtown hotel while on his way to his company’s annual investor conference.

In surveillance footage of the attack, a man wearing a hooded jacket is shown emerging from behind a car and shooting Thompson several times before fleeing the scene.

Police have described the killing as a “premeditated” and “targeted” attack.

Shell casings left at the scene were emblazoned with the words “deny,” “defend” and “depose”, an apparent reference to the title of a 2010 book about the tactics insurance companies use to avoid paying claims.

While police have not announced a motive in Thompson’s murder, his wife told US media that “there had been some threats” against her husband.

Thompson’s murder has sent shockwaves through corporate circles as well as drawn attention to the widespread public fury over the US health insurance industry’s treatment of people in need of medical care.

Since Thompson’s murder, thousands of people have taken to social media to celebrate the killing or express sympathy with the killer.

Many of those expressing glee over the murder have recounted experiences of the insurer declining to cover treatment for themselves or their family members.

In an Senate committee report released in October, US lawmakers accused UnitedHealthcare of using artificial intelligence to raise its prior authorisation denial rate for post-acute care from 10.9 percent in 2020 to 22.7 percent in 2022.

UnitedHealthcare is one of the biggest health insurers in the US, providing health coverage to more than 49 million Americans.

The company had revenues of $371.6bn in 2023, up nearly 15 percent from the previous year.

Thompson, who joined the insurer in 2004 and had served as CEO since 2021, received $10.2m in compensation the same year.