NYPD Releases Footage of UnitedHealthcare CEO's Killer Opening Fire

NYPD has clear footage of the killer who opened fire on UnitedHealthcare CEO Brian Thompson in Midtown Manhattan ... but only from behind the suspect.

Cops released the surveillance images captured Wednesday morning outside the Hilton hotel on 6th Ave and 54th Street ... and it shows 50-year-old Thompson strolling into the hotel by himself around 6:45 AM. The shooter walks up behind him, draws a handgun and starts shooting from less than 10 feet away.

It appears the suspect fired his weapon, which was fitted with a silencer, at least 3 times ... before fleeing into an alleyway on the other side of the street. Police say he made his getaway on a bicycle, which was captured on a different surveillance camera, and rode into Central Park ... just a few blocks away.

Witnesses have said the cold-blooded killer was masked, and had been waiting outside the hotel for at least several minutes before Thompson arrived. The footage seems to support NYPD's theory that this was a targeted hit.

The challenge for police is none of the surveillance images they've released have a clear view of the suspect's face -- he was wearing a hoodie with a gray backpack -- and the footage does not include any audio.

Cops say they recovered 3 9-millimeter rounds and shell casings from the crime scene. They're offering a $10,000 reward for any info leading to the suspect's arrest and conviction -- while also working with UnitedHealthcare to figure out a possible motive ... including any recent threats or disgruntled ex-employees of the health insurance giant.

Thompson was transported to a hospital, where he was pronounced dead.