WEST HEMPSTEAD, N.Y. (CBSNewYork) -- Everyone's worst nightmare played out in a few terrifying moments at a West Hempstead Stop & Shop.
Shots rang out. One person is dead, two others injured, and the gunman - on the run for hours - is now under arrest, a supermarket cart collector with a history of mental illness.
Terrified employees fled Stop & Shop on Cherry Valley Avenue at around 11:20 a.m. as shots rang out from upstairs offices.
"Three managers were shot inside the store. I heard probably five shots, and this is the offices on the second level," said one employee.
Watch: Nassau Police Share Update On Stop & Shop Active Shooter
"I'm a cashier, and I was right up, I was right up at the cash register, and I heard I think about six gunshots. I finishing waiting on my customer, she was almost done, and I ran out, I left, and I sat in my car in the parking lot. Then I asked the officer if I should leave. I'm over with all the employees sitting here," Cathleen Coughlin said. "I saw someone come out on a stretcher."
One shopper says she pulled up to a scene of chaos.
"People were coming running out and some man said to me 'Honey, honey, don't go in there. They said don't go in there, there's an active shooter,'" said West Hempstead resident Liz Lee.
"Frantic. Frantic. People just running with their carts," another shopper said.
An active shooter on the run for hour hours. Nassau Police descended on the West Hempstead neighborhood, locking down schools and colleges while searching for a shooter armed with a small handgun, wearing all black. Police released a picture of 31-year-old person of interest, Gabriel Dewitt Wilson, who was found at a Terrace Avenue, Hempstead apartment by the Nassau Police SWAT team.
"The subject tried to flee down through the first floor. He was then apprehended both by the Hempstead and Bureau of Special Operations at the police department," said Nassau Police Commissioner Patrick Ryder.
Authorities say the gunman took the life of a 49-year-old man. He was identified by Valley Stream South school officials as a father of two students. His grieving family asked for privacy.
Two other employees, gunshot victims, were taken to hospitals, conscious and alert, spoke with law enforcement.
"When he showed up to work today, he went straight down to an office on the second floor. At that time, he shot a male and female victim," Ryder said. "And then he went down to a second office, where he shot and killed one of the managers of the building.
WATCH: Chopper 2 Over Scene Of Deadly Stop & Shop Shooting
Roughly 100-200 shoppers were in the supermarket at the time, terrified and looking for cover.
"I was just shopping and I heard get out, get out. Police all over," said one.
Barbara Butterman was among a frightened group of shoppers and employees being rescued by police.
"We just sort of all banded together, and we were trying to figure out in the produce department, there are places to hide under the counter ... if the shooter came along that we had place to go," she said.
Workers were tearful and traumatized.
"Screaming, chaos, and they heard shots and then ran out of the store," said Deana Abondolo, Union President of Local 342.
Their union reps were on scene, calling for an end to gun violence now striking at essential workers in the workplace.
"When is this going to end in this country, where we have to worry about our members? Union members work very hard every day, and have people walk in with guns," said Kelly Egan of Local 342, United Food Commercial Workers.
"This is the worst nightmare ... We brought grief counselors with us, and we will be here for our members throughout, whatever they need," said John Durso, Union President of Local 338.
Watch Jennifer McLogan's report
Police say Wilson has a prior criminal record and had at least one mental health encounter with the county. Police say calls from the public helped lead them to him.
One shopper put it this way: West Hempstead has come into the real world - we are now a part of these mass shootings.
"We in Nassau County have watched on our television screens active shooters devastate communities. But today, that reality came home to Nassau County," Nassau County Laura Curran said.
Stop & Shop President Gordon Reid said the company was "shocked and heartbroken by this act of violence."
"Our hearts go out to the families of the victims, our associates, customers and the first responders who have responded heroically to this tragic situation," his statement continued.
Schools and other buildings in the area were placed under lockdown, and people were asked to stay inside while the search was underway.
Parents like Jorge Guevera tried to remain calm outside the Chestnut Street School in West Hempstead.
"I see the news and it's terrible," he told CBS2's Jennifer McLogan.
"I came to get my daughter. I don't know why they don't open the door yet. That makes me nervous," parent Mariella Pena said.
Gov. Andrew Cuomo said he was closely monitoring the situation and he directed the New Yok State Police to help with the investigation.
"I'm praying for the victims, and my heart breaks for their families and loved ones," he said in a statement.
Police say they are investigating the motive.
CBS2's Jennifer McLogan contributed to this report.
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