(Reuters) - New York City police were still searching for the man who killed UnitedHealth ( UNH ) executive Brian Thompson outside a Midtown Manhattan hotel early Wednesday. Here is what is known about the incident, Thompson, and the suspect:    

WHAT HAPPENED? HOW DID THE SUSPECT ESCAPE?

At about 6:45 a.m. ET on Wednesday, Thompson was walking from his hotel alone towards a Hilton hotel in Midtown Manhattan when a gunman approached from behind and shot him in the back.

Thompson staggered and fell to the ground. A witness is seen fleeing in surveillance video as the gunman, wearing a dark-colored hoodie and a backpack, approaches Thompson and fires a second time. His gun appears to jam, and after fiddling with the weapon, he resumed firing from a short distance.

The gunman then fled across the street. Following that, according to the New York Police Department, he got on a bike that he rode into nearby Central Park, where he was last seen. 

Police said the gunman arrived outside the hotel several minutes before Thompson and waited for him to walk past before firing, ignoring other passers-by.       

WHO WAS BRIAN THOMPSON?

Thompson, 50, lived in Maple Grove, Minnesota. He had been the CEO of UnitedHealthcare, UnitedHealth Group's ( UNH ) insurance unit, since April 2021. He was in New York for the company's annual investor conference when he was killed.

He had worked at different divisions of UnitedHealth ( UNH ) for about 20 years. His wife Paulette said in a statement that "Brian was an incredibly loving, generous, talented man who truly lived life to the fullest and touched so many lives."

Thompson graduated from the University of Iowa in 1997 with degrees in business administration and accounting, according to his LinkedIn page. Prior to becoming CEO of UnitedHealthcare, he was the head of its government programs business and before that its Medicare and retirement business.

UnitedHealth ( UNH ) is the largest U.S. health insurer. The company, along with Thompson and two other executives, were sued in May by a Hollywood, Florida, pension fund, which accused the company of insider trading after being made aware of a U.S. Department of Justice investigation into UnitedHealth.  

WHAT EVIDENCE HAVE THE POLICE FOUND? 

Surveillance video suggests that he used a silencer, but Chief of Detectives Joseph Kenny told reporters that could not be verified by that video alone. The gun has not been located. 

CNN reported that the killer dropped a phone and a bottle of water in an alleyway nearby. 

WHAT DO WE KNOW ABOUT THE SUSPECT? 

Investigators have not yet named a suspect, though CNN reported that police were searching a hostel in New York's Upper West Side where he may have stayed prior to the attack.

Police published a number of photographs of the suspect taken from video cameras in the area, including one with the gun raised and pointed toward Thompson and another of the suspect fleeing on a bike. He appears to be light-skinned and of average build. 

Other photos captured a glimpse of his eyes, brow and the bridge of his nose as he stood in a cafe. 

WHAT WAS THE MOTIVE?

Police do not yet know the motive.

The words "deny," "defend" and "depose" were carved into the shell casings found at the scene, police sources told ABC and the New York Post. Reuters has not independently verified that information. The words evoke the title of a book critical of the insurance industry published in 2010 titled "Delay Deny Defend: Why Insurance Companies Don't Pay Claims and What You Can Do About It."

Paulette Thompson told NBC News on Wednesday that he had been receiving threats related to his job, but was not specific. 

Police in Minnesota do not have any record of specific threats against Thompson, though Paulette Thompson in 2018 called police once when she saw the deadbolt turning on the front door of their home. Police found no sign of an attempted break-in.