>> kevin was a suspect that we needed to find out the validity of his statements, whether he had gunshot residue on his hands, whether he was even able to shoot a gun, given his physical disabilities. >> reporter: but a suspect? they checked his hands for gun powder residue. negative. >> you have to look at everybody, unfortunately. sometimes hurt feelings, but you have to get down to the facts, too. >> reporter: but facts can be tricky things. and in this case far more elusive than anyone might have imagined. many some clies were elusive, but some were right out in the front, like the two that dramatically narrowed down the circle of suspects. >> coming up. >> those are huge. it eliminates everybody down to only those people that have access to those two keys. >> when "dateline" continues. o >> when "dateline" continues