but rod mccutcheon, a toxicologist at the texas department of public safety crime lab, was willing tory. >> 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 and added an acid solution to dissolve all of the organic material. what was left was primarily sulfuric acid. in a process called colorimetric testing, he added hydrochloric acid and zinc to the mix. >> as it bubbles through this device, the arsenic will react and form if it's present a purplish violet color. the more arsenic present, the stronger the more purple the color is. >> rod mccutcheon's chemical cocktail made forensic history. conclusive can proof of the presence of arsenic. the depth of color in the reaction showed that cordelia norton ingested a massive amount of arsenic.