There's no evidence because no one bothered to investigate it to determine a cause. While Amazon didn't go to great lengths to cover up his death, I get the imp

There's no evidence because no one bothered to investigate it to determine a cause. While Amazon didn't go to great lengths to cover up his death, I get the impression the company didn't expend a lot of energy into determining what happened. The basic story of this article is that Integrity employees who work at Amazon's warehouses are expendable, second class citizens.