New York's mayor said Saturday "the net is tightening" on the man suspected of gunning down a top health insurance executive outside a Manhattan hotel before fleeing the city, as new evidence emerged in the brazen killing.

Mayor Eric Adams also said detectives know the name of the suspect who has been on the run since shooting UnitedHealthcare chief executive Brian Thompson at close range early Wednesday in a killing that has seized national attention.

Adams praised the manner in which investigators "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're going to bring this person to justice," he said, the New York Post reported.

The masked assailant was caught on camera entering a bus station in northern Manhattan following Wednesday's murder, but he could not be identified exiting the facility on foot, a police spokesman confirmed to AFP.

"They believe he's not in New York City," the spokesman added.

An image released Thursday of the smiling suspect was obtained from a youth hostel where the gunman apparently stayed before the hit,  with media reporting he had lowered his mask to flirt with a receptionist.

The FBI, which said it was assisting New York police, offered a reward of up to $50,000 for information leading to the suspect's capture.

New evidence emerged Saturday, a day after authorities located a gray backpack in Central Park thought to belong to the killer. Inside were two items: a jacket and Monopoly money, US media reported.

Police were also looking into the possibility that the shooter took the rare step of using a long-barrel veterinary gun — normally used to euthanize animals — to commit the murder.

Delay and deny

The gunman on Wednesday walked up behind Thompson of UnitedHealthcare — one of the country's largest medical insurers — and shot him dead in front of bystanders, in an audacious attack captured by a surveillance camera and now seen by millions.

Thompson was attending an investor conference in the Midtown business district.

Police have yet to suggest a motive and would not confirm media reports that the words "delay" and "deny" — language often used by insurance companies to reject claims — were written on shell casings found at the scene.

Video footage shows Thompson on the sidewalk outside the New York Hilton Midtown when a man in a hooded top, his lower face covered, approaches from behind, then fires several shots at his 50-year-old victim, who crumples to the ground.

Footage showed the suspect fleeing on foot, before getting on a bicycle, with police revealing he headed to Central Park.

Officers have confirmed that a cell phone as well as DNA from a coffee cup were recovered near the murder scene.

Absent an arrest, speculation has been rife that the gunman may have sought to take revenge for adverse medical coverage decisions made by the insurer.

UnitedHealthcare is a major player in the lucrative American health care market, and the parent group had revenues of $100.8 billion in the third quarter of the year.