>> if scoggin poisoned the norton sisters, no one could prove it. they had both been cremated. all that remained were their ashes. >> he believed he could burn up the evidence and he would be safe. >> in the average cremation, the body is subjected to temperatures of more than 2,000 degrees fahrenheit for up to three hours. virtually nothing remains. >> it takes a lot of temperature to reduce a body to nothing but a little pile of ashes. >> investigators called laboratories and universities around the country, but no one knew of any way to test cremated remains for forensic evidence. but rod mccutcheon, a toxicologist at the texas department of public safety crime lab, was willing to try. >> so i started thinking about the possibility of detecting arsenic in a cremated remains sample, and decided it might be possible. there were a lot of things to consider. >> mccutcheon knew that arsenic is actually a metal and some metals survive fire and intense heat. >> you may change its form from a solid to a gas but you aren't going to destroy the arsenic itself. >> so he took the sisters' ashes