NEW YORK — The masked gunman who stalked and killed the leader of one of the largest U.S. health insurance companies outside a Manhattan hotel used ammunition emblazoned with the words “deny,” “defend” and “depose,” a law enforcement official said Thursday.

The official was not authorized to publicly discuss details of the ongoing investigation and spoke to The Associated Press on the condition of anonymity.

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

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

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Investigation Uncovers Crucial Evidence

Investigators recovered several 9 mm shell casings from outside the hotel and a cellphone from the alleyway through which the shooter fled, NYPD Chief of Detectives Joseph Kenny had said earlier.

The killing and the shooter’s movements in the minutes before and afterward were captured on some of the multitudes of security cameras present in that part of the city.

The hunt for the shooter brought New York City police Thursday morning to at least two hostels on Manhattan’s Upper West Side, based on a tip that the suspected shooter may have stayed at one of the residences, according to a second law enforcement official briefed on the investigation, who requested anonymity because they were not authorized to discuss the ongoing search.

Two detectives arrived at the Kama Central Park hostel at 7 a.m. Thursday with a photo of the shooter and asked staff if they recognized the man, an employee confirmed to the AP. They did not, the employee said, and the detectives left. An employee at the nearby HI New York City hostel also confirmed that police had visited the location Thursday, but declined to provide further information.

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Motive Remains Unknown as Investigation Continues

The reason behind Thompson’s ambush killing remained unknown.

Police Commissioner Jessica Tisch said at a news conference Wednesday that while investigators had not yet established a motive, the shooting was no random act of violence. “Many people passed the suspect, but he appeared to wait for his intended target,” she said.

Investigators believe, judging from surveillance video and evidence collected from the scene, that the shooter had at least some prior firearms training and experience with guns and the weapon was equipped with a silencer, said one of the law enforcement officials who spoke with the AP.

Investigators are also looking into whether the suspect had pre-positioned a bike as part of an escape plan, the official said. The shooter fled on a bike and he was last seen riding into Central Park.

Authorities were running DNA and fingerprint analysis on items found nearby, including a water bottle, that they believe the suspect may have discarded, the official said.

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Intensive Search Underway for Suspect

Security camera video showed the killer approach Thompson from behind, level his pistol and fire several shots, barely pausing to clear a gun jam while the health executive tumbled to the pavement.

Other cameras captured the initial stages of the gunman’s escape. He fled the block across a pedestrian plaza, then escaped on the bicycle. Police used drones, helicopters and dogs in an intensive search, but the killer’s whereabouts remained unknown.

Police issued several surveillance images of the man, who wore a hooded jacket and a mask that concealed most of his face and wouldn’t have attracted attention on a frigid day. Some of the photos were taken at a Starbucks coffee shop shortly before the shooting. Police offered a reward of up to $10,000 for information leading to an arrest and conviction.

The insurer’s Minnetonka, Minnesota-based parent company, UnitedHealth Group Inc., was holding its annual meeting with investors to update Wall Street on the company’s direction and expectations for the coming year. The company ended the conference early in the wake of Thompson’s death.

Thompson, a father of two sons, had been with the company since 2004 and served as CEO for more than three years.

“Brian was a highly respected colleague and friend to all who worked with him,” UnitedHealth Group said in a statement. “We are working closely with the New York Police Department and ask for your patience and understanding during this difficult time.”

Thompson’s wife, Paulette Thompson, told NBC News that he told her “there were some people that had been threatening him.” She didn’t have details but suggested the threats may have involved issues with insurance coverage.

Eric Werner, the police chief in the Minneapolis suburb where Thompson lived, said his department had not received any reports of threats against the executive.

UnitedHealthcare is the largest provider of Medicare Advantage plans in the U.S. and manages health insurance coverage for employers and state and federally funded Medicaid programs.