when david waters' ex-girlfriend, patti steffens, read about david fry's murder in the newspaper, she immediately called the fbi. >> at first she wanted to tell us small bits and pieces. you have to understand this was a woman who was terrified. >> she gave investigators an important lead. three years earlier she said that david waters had rented a storage unit around the time the o'hairs disappeared and that waters had once gone there with this spray canister. laboratory tests on the canister revealed it had once contained bleach which is sometimes used to remove blood evidence. armed with a search warrant, police found a tiny red stain beneath a piece of aluminum under the wall. it was so small it was almost in visible. with blood from madalyn's son, bill for comparison, a mitochondrial dna test revealed the stain was a mixture of two people. madalyn murray o'hair and her son, jon murray. next the fbi searched jon's waters' apartment. >> we found documented that belonged to the o'hairs that were dated after david waters had been fired from their organization. >> mr. waters, himself