Bullet casings found at the scene when UnitedHealthcare’s CEO was shot by a masked gunman outside a busy New York City hotel bore the words “deny,” “defend” and “depose,” a top New York law The law enforcement officer was notified of the investigation, which NBC News confirmed Thursday.

Brian Thompson, 50, was killed in a “premeditated, pre-planned targeted attack” outside New York’s Hilton Midtown on Sixth Avenue in the heart of Manhattan, police said.

He was on his way to speak at the UnitedHealth Group investor conference when the gunman, who had been lying in wait for several minutes, came up from behind and shot him at least once in the back and at least once in the right calf, he said Police Commissioner Jessica Tisch press conference on Wednesday.

Police say they don’t yet know the shooter’s motive because they believe he is still at large.

ABC News was the first to report the words written on the bullet casings.

Despite known threats against him, Thompson did not travel with personal security personnel.

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“There were some threats,” Thompson’s wife, Paulette Thompson, told NBC News on Wednesday. “Basically, I don’t know, a lack of coverage? I don’t know the details. All I know is that he said there were some people who threatened him.”

Security video showed Thompson walking down the street wearing a blue suit. The gunman approached him from behind and opened fire, it was revealed. Thompson stumbled forward as a witness scrambled to safety. The gunman continued firing as Thompson fell to the ground, the video showed.

“The shooter then walks towards the victim and continues shooting. It appeared the gun was malfunctioning as he cleared the jam and began firing again,” said Detective Chief Joseph Kenny.

Thompson was pronounced dead at Mount Sinai West.

“The motive for this murder is unknown at this time, but based on the evidence we have so far, it appears that the victim was specifically targeted,” Kenny told reporters. “But at this point we don’t know why.”

Before the shooting, the gunman purchased a water bottle and two protein bars at a nearby Starbucks and discarded the items, according to a senior New York City police official briefed on the investigation.

Investigators recovered a video showing where the suspect discarded the items, and police collected them as evidence in the hope that it could help in the investigation, the official said.

Former FBI Supervisor Rob D’Amico said Wednesday that Thompson’s killing had all the hallmarks of a personal vendetta related to the victim’s company.

According to D’Amico, anyone could have found out the high-profile business figure’s whereabouts with a few quick Google searches. UnitedHealthcare’s website listed an investor conference scheduled for Wednesday, but did not provide a location.

“Even a layperson can tell that there’s so much on the Internet now and people are posting so much,” said D’Amico, now a security consultant.

No current or former UnitedHealth Group executives regularly receive company-sponsored personal security services, according to the insurance giant’s two most recent proxy statements. Companies must report security expenses for directors or corporate officers if the value exceeds $10,000 per year.

Two of UnitedHealthcare’s peers, Humana and Cigna, both said in their recent proxy statements that they provide personal security to executives. But SEC filings did not indicate which executives received that protection or how much was spent.

CVS Health, another major player in health insurance, requires its CEO to use company aircraft and a company driver as part of a disclosed “executive safety program,” regulatory filings show.