The incident happened around 9 p.m. Sunday night, on Wisconsin Highway. Officials said there usually was a manhole cover over the cesspool, a hole in the ground that collects waste from toilets and sinks.
"To the best of our knowledge, there was some sort of issue involving the manhole cover for the victim to be able to fall through," said Jeff Bressler, of the Smithtown Fire Department.
Zeqiri's 14-year-old cousin, who was also in the store, found his cousin in the cesspool in about 8 feet of water and ran to a nearby store for help. By the time he had returned, Zeqiri had disappeared in the water.
About 75 police and firefighters responded to the scene and pulled Zeqiri out and rushed him to the hospital, where he was pronounced dead.
An autopsy was scheduled for the teen, who lived in Central Islip.
Yvonne Lieffrig, Smithtown's attorney, said that the property owner had nine summonses pending for zoning violations involving "parking lot maintenance" but that none involved the cesspool.
Homicide detectives said that it does not appear the cover was removed intentionally, but that the investigation continues.
Andrew Mastrangelo, a spokesman for Canton, Mass.-based Dunkin' Brands Inc., said the company and franchisee Jesse Walia were saddened to learn of the death.
It's not the first time someone has died in a Long Island cesspool - typically a large hole in the ground lined with rocks to filter the sewage before it's absorbed into the earth and usually covered with a lid.
In June 2007, a landscaper was killed after driving a lawnmower into one at a Deer Park home. In July 2006, a worried woman who went to check on her 76-year-old aunt found her in a 10-foot-deep cesspool in the front yard of her Huntington home.
And in September 2001, a Huntington man practicing archery in his backyard with his children died when an 18-foot-deep cesspool caved in and swallowed him. Searchers soon found the body of Michael Lobasso, an agent with the U.S. Drug Enforcement Administration, but struggled for about 18 hours to pull it from the quicksand-like pool of muck.