'Deny,' 'defend' and 'depose': Police investigating words found on shell casings in CEO shooting, sources say

The search for an unidentified gunman who fatally shot UnitedHealthcare CEO Brian Thompson, and the investigation into a possible motive, remain ongoing Friday.

Thompson, 50, was shot Wednesday morning outside a Midtown Manhattan hotel, where the insurance group's investors conference was being held. The masked gunman appeared to be lying in wait outside the Hilton hotel before shooting Thompson at close range, police said.

Police said they are interviewing Thompson's colleagues and family about any potential specific threats while they investigate a motive into the shooting.

Evidence collected from the scene of the shocking shooting include shell casings with the words "deny," "defend" and "depose" written on them, according to police sources.

ABC News contributor Brad Garrett, a former FBI agent, said he believes the shooter is "trying to send a message" through the words.

"It strikes me that it has to do with insurance companies using those terms in some of their processes of turning down claims," Garrett told ABC News Live's Stephanie Ramos when asked about the words. "It's a common complaint by people of having claims denied, and so I think this shooter is trying to send a message that someone -- either himself or a loved one or someone close to him -- has been harmed by this insurance company."

"There wouldn't be, logically, any other reason," he added.

The words on the shell casings also echo the title of a 2010 book "Delay, Deny, Defend: Why Insurance Companies Don't Pay Claims and What You Can Do About It." Police are aware of the similarity, and are investigating whether one possible motive is anger at the insurance industry, sources said.

The book was written by legal scholar and insurance expert Jay Feinman, a professor emeritus at Rutgers Law School in New Jersey.

It explores abuses of auto and homeowners insurance to "avoid paying justified claims," according to its summary.

"Today the name of the game is delay, deny, defend: to improve their profits, insurance companies delay payment of justified claims, deny payment altogether, and defend their actions by forcing claimants to enter litigation," the book description states.

This strategy is not restricted to auto and homeowners insurance, the introduction states. "All insurance companies have an incentive to chisel their customers in order to increase profits," it says.

ABC News has reached out to Feinman for comment.

In a response to a post on X that mentioned his book and the words on the shell casings, Feinman said he has "no comment" to media inquiries.

Police are working to identify the gunman in the shooting and his whereabouts.

After the shooting, the perpetrator fled on foot into an alley, where a phone was recovered, then fled on a bike, according to NYPD Chief of Detectives Joseph Kenny.

Other evidence recovered from the scene includes a water bottle and candy wrapper, police sources said.

Police have also collected video of the suspected gunman all over the city, including in the subway, in cabs and a McDonald's, since he arrived in New York City on Nov. 24 on a Greyhound bus, sources told ABC News.

In each place, he paid with cash and he made sure to keep his mask on, which indicates to detectives he knew he was coming to the city to commit the crime, sources said.

Police have released several photos of the shooting suspect while asking for the public's help in identifying him. They include images of him unmasked taken from a surveillance camera at an Upper West Side hostel, where it appears the suspect shared a room with two other men, according to police sources.

UnitedHealthcare's parent company, UnitedHealth Group, the largest health insurer in the world, said they are "working closely" with the NYPD in the wake of the shooting.

"So many patients, consumers, health care professionals, associations, government officials and other caring people have taken time out of their day to reach out. We are thankful, even as we grieve," UnitedHealth Group said in a statement on Thursday. "Our priorities are, first and foremost, supporting Brian's family; ensuring the safety of our employees; and working with law enforcement to bring the perpetrator to justice."

"We, at UnitedHealth Group, will continue to be there for those who depend upon us for their health care," the statement continued. "We ask that everyone respect the family's privacy as they mourn the loss of their husband, father, brother and friend."