Bullets used by an unknown gunman to shoot and kill Brian Thompson, CEO of UnitedHealthcare Words were written on it Wednesday morning, CBS News has confirmed.

According to law enforcement officials, the words “deny,” “defend” and “depose” were seen on bullet casings recovered from the scene of the shooting in New York City. Officials said they are investigating whether the words refer to a possible motive involving insurance companies and their responses to claims. ABC News first reported this information.

A source briefed on the investigation said every word was carefully written in Sharpie and not etched into the cases. Officials are examining the covers to determine whether the words could be linked to a possible motive involving insurance companies and their responses to claims. Investigators believe they may be referring to “the three Ds of insurance” coined by the industry’s critics: “Delay,” “Deny” and “Defend.” The alliteration is a commentary on the tactics that opponents say insurance companies use to delay or deny claims from policyholders.

Thompson, 50, was shot multiple times before 7 a.m. ET on Wednesday by a masked gunman who fled the area before police arrived. The shooting occurred in a busy part of Manhattan outside the Hilton Midtown Hotel, where the executive was scheduled to attend a conference for UnitedHealthcare investors. Thompson had been staying at the Marriott across the street, authorities said.

Security footage showed him walking to the Hilton around 6:45 a.m. when a gunman, who police said had been lying in wait for several minutes, shot him at least once in the back and later at least once in the leg. In the video, the suspect was seen briefly approaching Thompson before crossing the street. He then set off on his bike to Central Park. Police recovered three live cartridges and three fired cartridge cases from the scene.

According to NYPD officials, police executed a search warrant Wednesday evening at a building on Manhattan’s Upper West Side that the suspect had entered earlier in the day carrying the backpack seen in video of the shooting. The building they searched is in the same area as the Frederick Douglass Housing Project, where the suspect was seen near surveillance cameras at 5 a.m. on the day of the shooting. Initially mentioning the shooter’s proximity to the Frederick Douglas Houses, police said they were seeking a warrant for a building in the area where officials believe the suspect stayed Tuesday through Wednesday. It was unclear whether surveillance tape that showed the suspect near the housing development before the shooting also showed him entering a building in the area.

After Thompson was killed, the suspect was seen in Central Park and video showed him leaving the building somewhere between 70th and 80th streets. The housing development is located about a block from the west side of the park, between 100th and 101st Streets. Police said she

The shooter remained at large Thursday morning. Authorities described him as a white male wearing a tan jacket, a black face mask and black and white sneakers. He also carried a gray backpack. The NYPD released additional images of the suspect later Wednesday, showing him at a Starbucks two blocks from the shooting, about 20 minutes before it happened. A law enforcement source told CBS News that he paid cash at the cafe.

Police told CBS News that they found unspecified “forensic evidence” at the Starbucks and that items recovered there would be examined for possible DNA and fingerprints. They also said they had recovered an “investigative value” cell phone in the alley near the shooting scene and were forensically examining it to see if it could be linked to the shooter.

Although authorities did not give a possible motive for the shooting, New York Police Commissioner Jessica Tisch called it a “premeditated, pre-planned, targeted attack” at a news conference Wednesday. Police did not immediately respond to reporters’ questions about whether Thompson knew enemies before his death or whether he was blamed for UnitedHealthcare’s lack of coverage by policyholders. Coverage issues sparked protests in Minnesotawhere the company is headquartered and Thompson lived.

According to police, Thompson had no security guard at the time of his murder.

Eric Werner, the police chief in Maple Grove, Minnesota, the Minneapolis suburb where Thompson lived, said his department had not received any reports of threats against Thompson, the Associated Press reported. But the CEO’s wife, Paulette Thompson, told NBC News on Wednesday that there had been “some threats” against her husband.

“Basically, I don’t know, a lack of reporting? I don’t know any details. All I know is that there were some people who threatened him,” she said.

While police combed through surveillance images and searched the area around the shooting for additional videos, UnitedHealthcare investigators and security guards also reviewed files to see if there were records of previous threats or recently fired or disgruntled workers, according to a law enforcement source.

Police have asked anyone who may know anything about the shooting or the shooter to either report their knowledge to Crime Stoppers or provide tips anonymously online. The agency is offering a reward of up to $10,000 for information leading to the arrest and conviction of the suspect.

This is a developing story and will be updated.