A former Marine, armed with an AK-47 assault rifle and an automatic pistol, fired indiscriminately in a New Jersey supermarket on Friday, killing two co-workers before turning the gun on himself.
The gunman was identified as 23-year-old Terence Tyler, a former Marine who worked at the Pathmark store for the last two weeks, the local WABC TV reported.
He fired shots which killed two people and then killed himself, Old Bridge mayor Owen Henry said.
"This is the worst phone call a mayor can receive," Henry said.
"You can prepare for these things but you can't prevent them. The gunman, an ex-Marine, had been working at the store for about two weeks," Henry was quoted by the New Jersey Star Ledger as saying.
The employee opened fire at the Pathmarket store in Old Bridge in New Jersey at around 4 am (local time) on Friday as some workers were preparing to open the store, Middlesex County Prosecutor Bruce Kaplan said.
Authorities said the man left the store around 3.30 am (local time) and returned a half-an-hour later with a handgun, AK-47 assault rifle and multiple ammunition magazines.
The man fired the rifle at the first workers he saw, killing an 18-year-old woman and a 24-year-old man as other workers hid, Kaplan said.
He fired at least 16 rounds; windows of the store were also smashed in the shootout. He then turned the gun on himself.
Authorities are investigating the motive of the shooting.
The victims were "not specifically targeted. I believe everyone in the store was a target," Kaplan said.
Nearly 12 to 14 night shift workers were present in the store, and some of them hid when the gunman opened fire. Responding officers discovered the bodies and evacuated the other employees to a nearby restaurant. Several of them were being treated for trauma at waiting ambulances.
No shots were fired by the police, as the incident was over by the time they arrived.
The incident comes just a week after a 58-year-old designer at an apparel store near Empire State Building shot and killed his former co-worker outside the iconic New York tourist destination.
Earlier in August, Wade Michael Page went on a shooting spree inside a gurudwara in Wisconson, killing six members of the Sikh community as they were making preparations for the Sunday morning prayer service.
In July, a masked gunman had killed 12 people and wounded 58 others when he opened fire during the screening of the recent Batman film The Dark Knight Rises in Aurora, Colorado.