Detectives scour thousands of hours of video for clues in slaying of UnitedHealthcare CEO Brian Thompson in NYC

NEW YORK — It was footage from surveillance cameras that told police that the man they suspect of killing an insurance executive on Wednesday had arrived in New York City on a bus more than a week before.

Surveillance footage showed the methodical execution of Brian Thompson, CEO of UnitedHealthcare. It led the police to the physical evidence at the core of their investigation, including the backpack that officers found in Central Park on Friday evening.

And it was the absence of surveillance video of the man thought to be the assassin that Friday finally yielded the news that he had most likely fled the city for parts unknown shortly after the shooting.

Hundreds of times over the course of 11 days, the man believed to be the killer, whose name remains a mystery to authorities, appears before one of the 60,000 cameras to which police investigators have access, a senior law enforcement official said Friday.

At 10:11 p.m. Nov. 24, he arrives at the Port Authority Bus Terminal on a Greyhound whose route started in Atlanta. He smiles for a desk clerk at a hostel on the Upper West Side. Around 6 a.m. Wednesday, he stops at Starbucks to buy water and snacks. After Thompson is shot by the entrance of the New York Hilton Midtown hotel at 6:44, the man flees on a bicycle, enters Central Park at 6:48, exits it a mile away at 6:56, strolls along the Upper West Side at 6:58 and catches a cab heading uptown precisely at 7 a.m. It’s all on video.

At 7:30 a.m., cameras show him entering an interstate bus station by the George Washington Bridge.

They do not show him leaving.

While investigators believe the suspect left the city, the mountain of visual information he amassed here has helped police create a profile of him that is guiding the investigation in New York and nationwide.

Cameras do not yield secrets on their own. In the headquarters of the Lower Manhattan Security Initiative, the midtown precincts that cover the area around the shooting and the offices of the Major Case squad, video recovery teams are scraping countless hours of footage. They are constructing a visual narrative one time-stamped snippet at a time, like old-time animators making a cartoon.

“You might have to look through 100 hours of video to get two minutes that’s usable,” Carlos Nieves, the Police Department’s assistant commissioner of public information, said at a news conference Friday night. The department’s chief of detectives, Joseph Kenny, added that there were hundreds of detectives working on every aspect of the case, including the videos.

The 60,000-camera network includes some installed across the city by police and by the Department of Transportation, along with thousands that belong to private entities — big banks, hotel chains, schools and real estate companies.

Any can be accessed remotely through the Police Department’s Domain Awareness System, created in part by the new commissioner, Jessica Tisch. The system coordinates data from many surveillance tools, including license plate readers and phone call histories, to help identify people.

When someone on a video recovery team gets a hit, they scroll back and forth through time and space, toggling to neighboring cameras as they try to keep the target in their sights.

And when the teams remotely viewing the cameras lose track of the person, the boots-on-the-ground work begins.

“Anywhere that creates a gap, somebody is physically walking around those neighborhoods, knocking on doors, going to stores,” the law enforcement official said. Security cameras like internet-connected doorbells mounted on the doors of apartment buildings often fill in those gaps, the official said.

A big gap in the narrative arose when the gunman pedaled into Central Park, where there are relatively few cameras.

Somewhere in the park, he ditched his distinctive backpack, which may or may not contain the weapon used in the killing. After searching the park for three days, officers said they found the bag Friday as the sun set and temperatures dipped below freezing, near a bridge over the 65th Street transverse. They did not open the bag; they took it to a crime lab for analysis.

On Friday night, the FBI offered a $50,000 reward for information leading to the arrest and conviction of the gunman.

Police had figured out the hostel the suspect stayed in, at West 103rd Street and Amsterdam Avenue, by working backward from the shooting to a snippet of him walking on West 100th Street before dawn. They figured he had been staying in the area and visited the few nearby lodgings.

On Nov. 24, the night he came to New York, footage showed that he made a foray to the Hilton — a possible reconnaissance run to the place where the killing would occur — between arriving at the Port Authority and checking into the hostel.

Information gathered by the camera network can be interrogated using search terms like “backpack” or “bicycle.” But those queries turn up so many false hits (picture how many food deliverers in a neighborhood are riding bikes and wearing backpacks) that they are of limited use, the official said.

The official said facial recognition software was not helpful in the search for the gunman, either. The Police Department’s limited recognition system is based on booking photos taken at arrests, so anyone who has no arrest record here will not be in the system.

As the detectives trace the gunman’s complete whereabouts and activities — if he slept eight hours a day, he spent something like 9,000 waking minutes in the city — they hope to learn something that helps crack the case.

“We think he’s a lone actor,” the official said, “but who knows what the video camera will ultimately reveal?”

Eryn Davis contributed reporting.