Police in New York are using facial recognition technology and a discarded cell phone to identify and track down the killer of a healthcare chief executive.

UnitedHealthcare boss Brian Thompson, 50, was fatally shot in the back on Wednesday morning outside the Hilton hotel in Midtown Manhattan.

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

They are focusing on a surveillance image taken in a branch of Starbucks just before the shooting.

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

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 light brown or cream-coloured 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.

New York Police Department (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.

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.

The words “deny,” “defend” and “depose” were discovered on the casings, police sources told ABC News.

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.

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.