NEW YORK — The masked gunman who stalked and killed the head of one of the largest U.S. health insurers had the words “deny,” “defend” and “depose” emblazoned on his ammunition, echoing a phrase used by industry critics, two law enforcement officials said Thursday.

The words were written in permanent marker, according to one of the officials, who were not authorized to publicly discuss details of the investigation into the shooting early Wednesday outside a Manhattan hotel and spoke to The Associated Press on the condition of anonymity.

With the gunman still at large, police also released photos of a “person of interest” wanted for questioning in connection with the killing of UnitedHealthcare CEO Brian Thompson.

The images, showing an unmasked man in the lobby of a Manhattan hostel, add to a collection of photos and video that have circulated since the shooting — including footage of the attack itself, as well as still frames of the suspected gunman stopping at a Starbucks beforehand.

Thompson, 50, died in a dawn ambush as he walked from his midtown hotel to the company’s annual investor conference at a Hilton across the street, blocks from tourist draws such as Radio City Music Hall, the Museum of Modern Art and Rockefeller Center, where the famed Christmas tree was lit Wednesday night. The reason for the killing remained unknown, but New York City police say evidence firmly points to it being a targeted attack.

The messages on the ammunition mimic the phrase “delay, deny, defend,” which is commonly used by lawyers and insurance industry critics to describe tactics used to avoid paying claims. It refers to insurers delaying payment, denying a claim and then defending their actions. Health insurers like UnitedHealthcare have become frequent targets of criticism from doctors and patients for denying claims or complicating access to care.

Investigators recovered several 9 mm shell casings from outside the Hilton and a cellphone from the alleyway through which the shooter fled. Inside a nearby trash can, they found a water bottle and protein bar wrapper that they say the gunman purchased from Starbucks minutes before the shooting. The city’s crime lab is examining those items for DNA and fingerprints.

The killing and the shooter’s movements in the minutes before and afterward were captured on some of the multitude of security cameras in that part of the city. The shooter fled on a bicycle and was last seen riding into Central Park.

A tip that the shooter may have stayed at a hostel brought police Thursday morning to at least two such establishments on Manhattan’s Upper West Side, according to one of the law enforcement officials briefed on the investigation. The photos made public Thursday were taken in the lobby of the HI New York City hostel.