NEW YORK — Authorities are intensifying their search for the gunman who fatally shot UnitedHealthcare CEO Brian Thompson, as new clues emerged nearly four days after the brazen attack that has sent shockwaves through corporate America.

Investigators believe the suspect left New York City on a bus shortly after the shooting but left behind a backpack in Central Park, now under forensic analysis.

Thompson, a father of two and head of the nation’s largest health insurer, was killed outside a hotel during the company’s investor conference.

Surveillance footage captured the masked assailant fleeing the scene on a bicycle before switching to a taxi en route to a bus terminal.

Police suspect the shooter, who concealed his identity almost entirely during his time in the city, used fake identification and paid in cash for accommodations at a Manhattan hostel.

Chief of Detectives Joseph Kenny revealed chilling details about the attack, noting that the weapon may have been a veterinary pistol and that the ammunition bore the words “delay,” “deny,” and “depose” — a possible reference to criticisms of insurers' practices.

The FBI has offered a $50,000 reward for information leading to an arrest, while police continue to analyze DNA evidence and track the gunman’s movements.

The killing has prompted health insurers nationwide to reassess security protocols, with some companies closing offices temporarily and removing executive photos from websites.

Thompson’s death marks a tragic end to his nearly two-decade career at UnitedHealthcare, where he served as CEO for over three years.

The company has pledged support for Thompson’s family and vowed cooperation with investigators in the pursuit of justice. — Agencies