He died of a heart defect, which is rare, but that no one considered a possibility in a young and in shape guy. One of the major flaws for the prosecution was how the tissue evidence was processed. Apparently they sent the tissues to a military lab that didn't test human samples. So they could technically run the right tests but lacked knowledge to interpret and consider all possibilities.
Cindy went to prison because of misread lab results, no one seriously considered natural causes, and she got a boob job.