The shooting happened on an upper level of a Stop & Shop grocery in the community of West Hempstead, while a couple hundred people were inside the store, police said.
Gabriel DeWitt Wilson is a “person of interest” who “we believe is the shooter,” Nassau County Police Commissioner Patrick Ryder said.
“He left the scene, and he was witnessed still carrying the handgun,” Ryder told reporters.
Wilson, about 30, was last seen heading west on a nearby turnpike, police said. Police said Wilson is about 6 feet 2 inches tall and was wearing a black baseball cap and a black sweatshirt.
He had worked at the store, but investigators aren’t certain whether he still was employed there, Ryder said.
The shooting killed a 49-year-old store employee, police said. The two wounded survivors were taken to a hospital, and were conscious and speaking with law enforcement officers, authorities said.
Authorities say they do not know a motive for the shooting.
West Hempstead is about a 10-mile drive east of the New York City borough of Queens, officials said.
Police are canvassing the area, and nearby schools are on lockdown and have been told to secure their buildings, Nassau County spokesperson Christine Geed said.
This story is developing. Check back for updates.