thomas sprayed the notes with ninhydrin, a chemical that acts with the amino acid in perspiration. >>aced those letters and envelopes into a humidifying chamber. under the conditions, the prints will develop like a photograph on photograph paper. >> it revealed that dorothy was not sweating when she wrote the notes. something that usually occurs when someone intends to end their own life. >> and told him, that they needed to take another look at this case. because there was something wrong. >> but perhaps the most definitive proof would come from the envelope flaps. who had licked them? dorothy or chris? ♪ ♪ great rates for great rides. geico motorcycle, see how much you could save. >>> investigators wanted to know who had licked and closed the envelopes that held dorothy davis' suicide notes. to find out, scientists needed dorothy's dna for comparison. unfortunately her body had already been cremated so they had to reconstruct her dna profile by analyzing the dna from both her parents and her two children. >> her dna type was determined by cross-referencing the possible types that sh

the pizza box was sprayed with ninhydrin which reacts with amino acids and sweat and exposes fingerprintspeople had handled the box, which created potential problems. >> it's very difficult to backtrack and find everybody who had access to the pizza box when it was on the shelf, and you know, the pizza delivery boy and all these other people. >> the prints were compared to people known or thought to be involved in the case -- karen, tim permenter and karen's ex-boyfriend, roc herpich. roc's prints weren't found but tim permenter's were. >> we talked to roc. he was with a whole bunch of people, including his new family at the time. >> i didn't kill her. i didn't kill her. >> how does it look? you're over there, when you say you weren't? >> i don't know. >> contradicted his story simply the fact that his prints were on that box, he must have touched it after it was delivered. >> but to get a conviction, investigators needed more. >> eating pizza doesn't make him a murderer. ing with chantix. as a police officer, i've helped many people in the last 23 years. but i needed help in quitting smo

. >> to look for forensic evidence criminalists saturated the letter with ninhydrin, a chemical that reacts with amino acids from skin oils. then the letter was placed in a humidity chamber for several hours. the moisture in the chamber accelerated had chemical process eventually revealing an almost perfect thumbprint. this was photographed and then compared to prints in every fingerprint database available. >> they did databases for city employees, department of motor vehicle, postal workers, including police officers. and nothing. no hits. >> there had been no witnesses. none of the surviving victims could give a description. and the only forensic evidence was a single fingerprint. zodiac claimed that only the constellations orion and the seven sisters could stop him. new york police hoped to add themselves to the list. >>> the zodiac killed one man and wounded three hours in new york city. and for some unexplained reason, he struck only on nights when the constellations orion and the seven sisters were not in the sky. just as unusual was the fact >>> the zodiac killed one man and