Barry Jennings died shortly after he gave his witness evidence of the collapse of Building 7 at the World Trade Centre on 9/11. His death has never been explained and investigators paid to discover the truth returned their fees and refused to investigate further.
He died years later. 2 days before the "official" report came out.
He was threatened numerous times for speaking out. He even recanted much of what he said. But he mysteriously died anyway.
Watch him in the consecutive editions of Loose Change.
You'll figure it out. His story changes and the film makers talk about the threats he was receiving.