Steven Nelson, 55, the manager of the Legal Sea Foods at the Walt Whitman Shops in Huntington Station died Saturday night after falling unconscious in the basement of the restaurant, which was filled with customers and staff at the time.
A.J. Carter, a spokesman for the town of Huntington, said Sunday the fire marshal determined the cause of the leak was a faulty flue, the New York Daily News reported.
"The issue was in the basement, where the manager ... was overcome," Carter said.
Citing a co-worker it did not identify, the newspaper said Nelson was felled when he went to the basement to investigate the odor of gas.
The report said Legal Sea Foods assistant manager Megan Smith, who survived, was overcome by gas when she went looking for Nelson, a father of two.
"She (Smith) went downstairs to inspect and disappeared," the co-worker said. "That's when we knew something was wrong. People kept disappearing down there."
Suffolk County police Lt. Jack Fitzpatrick said Sunday the carbon monoxide appeared to have been confined to the basement.
"It does not appear to have made it in the area of the restaurant where the customers were," he said.
Another 28 people were taken to hospitals for treatment of the effects of the invisible but deadly gas.
Fitzpatrick said no customers were harmed. The victims were all restaurant employees or emergency personnel who had rushed to the scene.
Nevertheless, Legal Sea Foods and two other restaurants were quickly evacuated after Nelson collapsed.
"They told us to leave because of a gas leak," Cheesecake Factory patron Kathy Sella told WNBC-TV, New York. "I didn't want to blow up or anything like that. We were at the bar having a glass of wine and then, one of the waitresses, she said you have to leave."
A summons has been issued requiring the restaurant to repair faulty equipment before it can reopen.