UnitedHealthcare's CEO was shot and killed Wednesday in a “brazen, targeted attack” outside a Manhattan hotel where the health insurer was holding its investor conference, police said, setting off a massive dragnet hours before the annual Rockefeller Center Christmas tree lighting nearby.

Brian Thompson, 50, was shot around 6.45 am as he walked alone to the New York Hilton Midtown from a nearby hotel, police said. The shooter appeared to be “lying in wait for several minutes” before approaching Thompson from behind and opening fire, New York City Police Commissioner Jessica Tisch said. Police had not yet established a motive.

“Many people passed the suspect, but he appeared to wait for his intended target,” Tisch said, adding that the shooting "does not appear to be a random act of violence.”

Surveillance video reviewed by investigators shows the shooter emerging from behind a parked car, stopping and pointing a gun at Thompson's back, holding it with two hands and firing multiple times from several feet away. The suspect continues firing, interrupted by a brief gun jam, as Thompson stumbles forward and falls to the sidewalk. The shooter is then seen walking past Thompson and out of the frame.

“From watching the video, it does seem that he's proficient in the use of firearms as he was able to clear the malfunctions pretty quickly,” NYPD Chief of Detectives Joseph Kenny said.

Thompson was shot at least once in the back and once in the calf, Tisch said.

The shooter, who police said appeared to be a man wearing a jacket, face mask and carrying a backpack, fled on foot before pedaling an e-bike into Central Park a few blocks away. The suspect remained at large Wednesday afternoon, sparking a search that included police drones, helicopters and dogs.

“We are deeply saddened and shocked at the passing of our dear friend and colleague Brian Thompson, the CEO of UnitedHealthcare," the insurer's Minnetonka, Minnesota-based parent company, UnitedHealth Group Inc., said in a statement.

“Brian was a highly respected colleague and friend to all who worked with him,” UnitedHealth Group said. "We are working closely with the New York Police Department and ask for your patience and understanding during this difficult time.”

Police issued a poster showing a surveillance image of the suspect pointing what appeared to be a gun and another image that appeared to show the same person on a bicycle. They offered a reward of up to $10,000 for information leading to an arrest and conviction.

Thompson's wife, Paulette Thompson, told NBC News that he told her “there were some people that had been threatening him.” She said she didn't have details but suggested the threats may have involved issues with insurance coverage.

Eric Werner, the police chief in the Minneapolis suburb where Thompson lived, said his department had not received any reports of threats against the executive.

The killing shook a part of New York City that's normally quiet at that hour, happening about four blocks from where tens of thousands of people were set to gather for Wednesday night's tree lighting. Police promised extra security for the event, which will go on as scheduled.

The hotel is also a short walk from other tourist sites, including the Museum of Modern Art, and is often dense with office workers and visitors on weekday mornings. Many security cameras are nearby.

“We're encouraging New Yorkers to go about their daily lives and their daily business but to be alert,” NYPD Chief of Department Jeffrey Maddrey said.

Investigators recovered several 9 mm shell casings from outside the hotel and a cellphone from the alleyway through which the suspect fled. They were also searching Thompson's hotel room, interviewing his UnitedHealthcare colleagues and reviewing his social media, Kenny said.

Police said the e-bike that the shooter used to ride into Central Park came from the city's bike-share program, CitiBike. A spokesperson for Lyft, which operates the program, said the company had not yet been contacted by police.

Health care giant UnitedHealth Group was holding its annual meeting with investors to update Wall Street on the company's direction and expectations for the coming year. The company ended the conference early in the wake of Thompson's death.

“I'm afraid that we — some of you may know we're dealing with a very serious medical situation with one of our team members,” a company official told attendees, according to a transcript. “And as a result, I'm afraid we're going to have to bring to a close the event today. ... I'm sure you'll understand.”

Thompson had served as CEO for more than three years and had been with the company since 2004.

UnitedHealthcare is the largest provider of Medicare Advantage plans in the U.S. and manages health insurance coverage for employers and state-and federally funded Medicaid programs.

Minnesota Gov. Tim Walz tweeted that the state is “sending our prayers to Brian's family and the UnitedHealthcare team.”

“This is horrifying news and a terrible loss for the business and health care community in Minnesota,” the Democrat wrote.