The gunman, who fled and set off a manhunt, was identified by the police as Sang Ho Kim, 63, of Fresh Meadows, Queens.

The shooting occurred just after 10 a.m. at a light fixture company on South Street in East Garden City, N.Y., only blocks from the Roosevelt Field mall. Shortly after, there was a strong police response.

Streets were closed, shoppers were screened as they left the mall, schools were locked down, and vehicles were stopped and searched. With a recent bloody terrorist attack on a mall in Kenya and a mass shooting at the Washington Navy Yard still in the news, many residents were alarmed when they saw the burst of law enforcement activity.

Steven Skrynecki, the Nassau County police chief, held an afternoon news conference to try to put to rest any fears that the shooting was a prelude to something larger.

"There is nothing to suggest that this individual is on a random shooting rampage," Chief Skrynecki said.

While the investigation is in its early stages, he said, the police believe that Mr. Kim knew his victims and was angry about a business deal.

"The motive here appears to be work related," Chief Skrynecki said. After the shooting, he said, Mr. Kim drove off in a white 2008 Honda Pilot. The chief then cautioned, "We believe that this suspect is armed and very dangerous."

The owner and an employee of the light company, Savenergy, were shot. The police did not immediately release their names, and it was unclear who had died.

A woman who identified herself as Mr. Kim's wife but who declined to give her name said in a telephone interview that her husband was "victimized" by his boss, the owner of Savenergy. She said her husband and the owner had been good friends for more than a decade through their church.

Sobbing and speaking in Korean, she said her husband was being forced to resign from his job installing LED lights as a contractor for the company. She said he was owed more than $10,000.

"He couldn't sleep well," she said. "His chest filled with anger."

On Wednesday morning, when her husband left their home and headed to the office in Garden City to try to settle the dispute, she said, she became concerned.

"I had a strange feeling," she said, adding that she called him four times, "and he didn't pick up the phone."

In their hunt for the gunman, the police searched the campuses of Nassau Community College and Hofstra University. They were assisted by the New York Police Department and the Federal Bureau of Investigation.

Jasmine Alston, 20, who works at the Macy's at the Roosevelt Field mall, said that she was let out of the building after her shift ended at 1:45 p.m. but that the mall itself was still closed at that time to people seeking to enter. She said the shutdown was uneventful: no announcements were made, and Macy's workers learned of the lockdown from customers or colleagues who called from outside. Even after becoming aware, she said, "some people were still shopping."

Jiha Ham and Michael Schwirtz contributed reporting.