An urgent manhunt continued Thursday in New York City as police combed a vast network of private and public surveillance cameras, pursuing leads in search of the person who shot and killed UnitedHealthcare CEO Brian Thompson the previous morning.

Investigators used drones and dogs and searched data on publicly used electric bicycles made by Citi Bike as the suspect remained at large after what police chiefs said was a targeted killing.

On Thursday morning, ABC News reported, citing police sources, that police were on the trail of a suspect.

Clues included a cell phone, footage of the suspect in the Upper West Side neighborhood and shell casings from bullets found at the crime scene with the words “deny,” “defend” and “depose,” according to unnamed sources who also spoke to ABC News.

“This does not appear to be a random act of violence,” New York City Police Commissioner Jessica Tisch told reporters. “Everything indicates that this was a premeditated, planned and targeted attack.”

Thompson was killed around 6:40 a.m. ET on Wednesday by a man in black who was carrying a gray backpack and whose face was covered up to his nose. Police used the word “he” when referring to the suspect.

The man in question had pointed a silenced pistol at Thompson’s back and shot the manager at least once in the back and calf just as he was about to enter a Hilton hotel in midtown Manhattan for an annual investor conference.

As Thompson collapsed on the sidewalk and jammed the gun, the man — who police say is “familiar with firearms” — quickly moved away and continued shooting.

The suspect then fled to nearby Central Park on an e-bike. As of Thursday, there had been no arrests in the case and police were offering a $10,000 reward for information.

Since Wednesday, police have also discovered footage of the man near the Frederick Douglass public housing project on Manhattan’s Upper West Side around 5 a.m. ET, ABC News reported.

The suspect’s motives remain unknown. Thompson’s widow said her husband had received threats. However, such incidents are not uncommon in controversial industries.

“There were some threats,” Paulette Thompson told NBC News. “Basically, I don’t know, a lack of coverage? I don’t know the details. All I know is that he said there were some people who threatened him.”

UnitedHealthcare is a subsidiary of UnitedHealth Group, one of the largest companies in the United States. The industry insures tens of millions of people with private health insurance.

The need for private health insurance is a fact of life in the United States, but it is often a thorn in the side of Americans and insurers are often accused of unfairly denying coverage. The company was also the subject of an insider investigation and unfair trade practices investigation, according to Fox Business News.

Thompson’s killing quickly sent shockwaves through the corporate world, with company security chiefs meeting for a conference call Wednesday.

“Many of my colleagues today are sitting down with the leaders of their executive protection teams and their security leadership teams and reassessing what they are doing and what they are not doing,” Dave Komendat, president of Seattle-based Komendat Risk Management Services, told New York Just.

Another security executive, CEO Michael Julian of MPS Security & Protection, told Axios, “I’m just shocked the guy didn’t have a protection unit.”

Thompson is survived by his wife Paulette and two sons.

The Associated Press contributed reporting