New York City police officers are using facial recognition technology and a discarded cell phone to identify the man who shot and killed UnitedHealthcare chief executive Brian Thompson Wednesday morning.

Thompson, 50, was fatally shot in the back just before 07:00 EST (12:00 GMT) outside the Hilton Hotel in Midtown Manhattan.

The attacker fled the scene without taking any of Thompson's belongings. Police believe he was targeted in a pre-planned killing.

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

How did the shooting and escape happen?

The shooting took place at about 06:45 EST (11:45 GMT) in a busy part of Manhattan close to Times Square and Central Park. Thompson had been scheduled to speak at an investor conference later in the day.

According to police, the suspect - who was clad in a black face mask and cream jacket - appeared to be waiting for Thompson for five minutes outside the Hilton hotel where he was expected to speak.

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

NYPD Chief of Detectives Joseph Kenny have revealed that the suspect's weapon appeared to malfunction, but that he was able to quickly fix it and continue shooting.

Video shows him fleeing the scene on foot; he was last spotted in Central Park on an electric bicycle

The investigation

So far, the investigation into Thompson's killing has centred on a few clues that police are using to identify the suspect.

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

While he is masked in the image, police sources told CBS, the BBC's US partner, that the mask is pulled down far enough so that his eyes and part of his nose can be seen.

With that, investigators are using facial recognition software to try to find a match.

Additionally, police are testing three bullet casings and three live rounds found at the scene for DNA.

A cell phone was discovered in an alley along the suspect's escape route. Police say they are "working through" the phone.

Investigators also said they would search Thompson's room at the nearby Marriott, which is down the street from where the incident took place.

Motive remains a mystery

Investigators have so far not identified a motive in the killing, although police did note that the assailant fled without taking any of Thompson's belongings.

In an interview with MSNBC, Thompson's wife said that there had "been some threats" against him earlier, although she was unable to provide details.

"I just know that he said there were some people that had been threatening him," she said.

According to police in Thompson's hometown of Maple Grove, Minnesota, there had previously been one suspicious incident at his home in 2018.

The incident was cleared with no criminal activity detected. No additional details were provided.