Police in New York have released two photos of an unmasked person being questioned over the murder of a health care executive.

UnitedHealthcare CEO Brian Thompson, 50, was fatally shot in the back Wednesday morning outside the Hilton hotel in midtown Manhattan.

The attacker fled the scene without taking Thompson’s belongings. Police believe the victim was a pre-planned murder.

To track down the suspect, investigators are also using facial recognition technology and bullet casings with cryptic messages. They have not yet revealed a motive for the shooting.

Here’s what we know about the suspect and the investigation.

The shooting took place around 6:45 a.m. EST (11:45 a.m. GMT) in a busy part of Manhattan near Times Square and Central Park. Thompson was scheduled to speak at an investor conference later in the day.

According to police, the suspect – who was wearing a black face mask and a tan or cream jacket – appeared to wait for Thompson for five minutes outside the Hilton hotel where he was scheduled to speak.

Thompson, who arrived on foot, was shot in the back and leg and pronounced dead about half an hour later at a local hospital.

New York Police Department (NYPD) Chief Detective Joseph Kenny has revealed that the suspect’s gun appeared to jam, but he was able to quickly repair it and continue firing.

CCTV footage appears to show the shooter had a silencer, also known as a silencer, attached to his pistol, BBC Verify has found.

New York City Mayor Eric Adams – a veteran of the NYPD – told MSNBC that the use of a silencer was unprecedented in his career.

“I’ve never seen a silencer,” he said. “It was really something shocking for all of us.”

Investigators reportedly believe the firearm was a BT Station Six 9, a weapon said to be based on pistols used by Allied special forces during the Second World War.

Police reportedly visited gun stores in Connecticut to find out where the gun was purchased.

After the shooting, a video shows the suspect fleeing the scene on foot. Officials initially said the suspect was using a Lyft electric Citi bike.

But Lyft, which owns and operates Citi Bike, later said the NYPD had informed it that one of its vehicles had not been used, according to the BBC’s US partner CBS News.

So far, the investigation into Thompson’s murder has focused on a few clues that helped police identify the suspect.

Officials released two images Thursday of an unmasked man who the NYPD said was “wanted for questioning” in connection with the murder.

Law enforcement sources told CBS that the person likely used a fake ID to check into a hostel in the area. The name used is fake and is not believed to belong to an actual person.

Investigators believe the person involved took a bus from Atlanta, Georgia, to New York days before the shooting, CBS reports, citing a person briefed on the investigation. It is unclear whether the person boarded the bus in Atlanta or later during a stop.

It is unclear whether this is the same person as the suspect.

Police previously said the suspect was photographed at a nearby Starbucks just minutes before the shooting.

While he is masked in the picture, police sources told CBS that the mask was pulled down to the point where his eyes and part of his nose were visible.

The investigators use facial recognition software to find a match.

So far, investigators have not identified a motive for the killing, although police determined that the attacker fled without taking Thompson’s belongings.

In addition, police are testing three bullet casings and three live cartridges found at the crime scene for DNA.

The words “deny,” “defend” and “depose” were discovered on the casings, two law enforcement sources told CBS.

Investigators believe this could be a reference to the “three Ds of insurance” – a well-known reference from industry opponents.

The terms refer to tactics used by insurance companies to deny payment claims from patients in the complicated and largely privately run American health care system.

The words are similar to, but not exactly the same as, the title of a book called Delay, Deny, Defend: Why Insurance Companies Don’t Pay Claims and What You Can Do About It.

Published in 2010, the book was written by Jay Feinman, a law professor at Rutgers University in New Jersey. It’s intended to be an exposé of the insurance industry and a guide for Americans on how to navigate the system.

Professor Feinman declined to comment when contacted by the BBC.

A cell phone was discovered in an alley along the suspect’s escape route. Police say they are “searching” the phone.

A coffee cup believed to have been discarded by the suspect was also examined for fingerprints and sent to an NYPD crime lab in hopes that it could help reveal his identity or unravel a chain of events.

Investigators also said they executed a search warrant at a location on Manhattan’s Upper West Side that he had entered earlier in the day.

The location is near the Frederick Douglas housing project, where police say surveillance video showed the suspect outside around 5 a.m. the morning of the crime.

Police previously said they would also search Thompson’s room at the nearby Marriott, which is on the same street where the incident occurred.

Thompson joined UnitedHealth, the largest private insurer in the United States, in 2004 from accounting firm PricewaterhouseCoopers.

He rose through the ranks to become CEO in 2021 and led the company through some very profitable years.

In an interview with MSNBC, Thompson’s wife said there had been “some threats” against him previously, but could not provide details.

“All I know is that he said there were some people who threatened him,” she said.

According to police in Thompson’s hometown of Maple Grove, Minnesota, there had already been a suspicious incident at his home in 2018.

The incident was solved and no criminal activity was detected. No further details were provided.