The shooting took place at an upper level of a Stop & Shop grocery store in the West Hempstead community while several hundred people were in 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 witnessed him still carrying the gun,” Ryder told reporters.
Wilson, about 30, was last seen on a nearby detour westward, police said. Police said Wilson was about 6 feet tall and was wearing a black baseball cap and a black sweatshirt.
He worked at the store, but investigators are not sure if he was still working there, Ryder said.
Police have killed a 49-year-old store employee. The two wounded survivors were taken to a hospital and were conscious and spoke to law enforcement.
Authorities say they do not know the motive for the shooting.
West Hempstead is about ten miles east of the New York City borough of Queens, officials said.
Police are recruiting the area, and nearby schools have been closed and they have been told to secure their buildings, Nassau County spokeswoman Christine Geed said.
This story unfolds. Check back for updates.