It happened in Manorhaven on Monday, July 1, according to Nassau County Police.
At approximately 11:45 a.m., two men were working on demolition for a Kirkwood Road home when a concrete wall collapsed on them.
One of the men, age 56, was taken to a nearby hospital with minor injuries.
The second man, age 20, went into cardiac arrest while en route to the hospital.
He was pronounced dead by hospital staff.
Police said the investigation into the incident is ongoing.
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