The shooter was identified as Sang Ho Kim, 63, Newsday reported. Police said he was a vendor for Savenergy Inc., an importer of energy-efficient lighting fixtures in East Garden City on Long Island.
All Garden City schools, Nassau Community College and the Roosevelt Field mall were locked down for several hours after the shooting. School officials said students had a normal day, but no one was allowed to enter or leave the buildings until the lockdown was lifted at the end of the school day.
Nassau County Police Chief Steven Skrynecki said at a news conference the owner of Savenergy was in critical condition after surgery. The company's website identifies the founder as John Choi.
Skrynecki said Kim had a "disgruntlement between him and the company." He said Kim is believed to have a weapon and described him as "very dangerous," although he said he does not believe the public is at risk.
At the mall, police told shoppers who wanted to leave to stay inside and those who drove into the parking lot to stay in their vehicles. The lockdown was lifted in the early afternoon.
"This is terrifying," Nancy Petrillo of Garden City told Newsday. "After what happened in Kenya, everyone is already on edge."
Garden City is a village on Long Island about 18 miles east of Manhattan.