Investigators released pictures showing the face of the man they believe killed Brian Thompson outside a Midtown hotel. They said the words “delay” and “deny” were written on bullet casings collected at the murder scene.

The cameras caught the gunman standing alone for five minutes on West 54th Street, ignoring the early-morning rush of people streaming by.

They caught him again as he stood in the dark at 6:44 a.m. and locked onto his target, Brian Thompson, the chief executive of UnitedHealthcare, who was walking on the other side of the street.

And they captured video of the gunman, who was dressed in black and wearing a gray backpack, crossing the street and walking up to Mr. Thompson. He appeared calm as he raised a gun, fired several times and then walked away.

The seconds before Wednesday morning’s shooting of Mr. Thompson, the fatal moments and the immediate aftermath were all captured on surveillance cameras, leaving investigators with a trail of digital evidence to help search for a man who was “proficient” with firearms, according to Joseph Kenny, the chief of detectives for the New York Police Department.

After the Sept. 11 attacks, the Police Department, with help from the federal government, poured resources into expanding its surveillance capabilities. New York City now has a vast system of cameras, both public and private, that the police can scour to locate people.

The city has “investigatory capabilities that are above and beyond most municipalities,” said Brittney Blair, a senior director in the investigations and disputes practice at K2 Integrity, which advises companies on risk management and security.

On Wednesday, cameras inside a Starbucks two blocks from the crime scene that the gunman visited minutes before the shooting captured his partially hidden face.

Others showed the gunman waiting for Mr. Thompson, and then recorded him fleeing on a bicycle into Central Park, where he disappeared.

By late Wednesday, the police had released at least five images of the suspect, but had not announced arrests. They had not identified the shooter or a motive.

Jeffrey Maddrey, the chief of department, said the police would use its aviation unit, dogs and drones to find the killer.

Investigators would work backward to create a timeline, talking to Mr. Thompson’s friends, colleagues and family, scrutinizing his social media accounts and analyzing surveillance footage around Midtown, the police said.

“An incident like this happens, we don’t spare any expense,” Chief Maddrey said.

The footage revealed a chilling encounter between the seemingly calm gunman and an unsuspecting executive from Minnesota.

The gunman raised the weapon, heedless of a woman standing nearby on the sidewalk. He fired several times, hitting Mr. Thompson in the calf and back, as the woman ran away, according to the footage.

Mr. Thompson barely had time to whirl and face his attacker before crumpling to the ground. The gunman fiddled with his weapon, which had appeared to jam, and shot again as he walked toward Mr. Thompson.