Latent Prints in the 1933 Hamm Kidnapping
A Byte Out of History
The story begins like an old gangster flick: a gang of criminals and an unexpected kidnapping.
On a warm summer evening in 1933, William A. Hamm, Jr., President of the Theodore Hamm Brewing Company, was working at his office in St. Paul, Minnesota. He had just exited the building when he was grabbed by four shadowed figures and pushed into the back of a car. What he didn't know was that he had been kidnapped by members of the Barker/Karpis gang, for a ransom of over $100,000.
Hamm was taken to Wisconsin, where he was forced to sign four ransom notes. Then he was moved to a hideout in Bensenville, Illinois, were he was held prisoner until the kidnappers had been paid. Once the money was handed over, Hamm was released near Wyoming, Minnesota. The plan was perfect and went off without a hitch...almost.
Enter the FBI Crime Lab. On September 6, 1933—almost precisely 70 years ago--and using a then state-of-the-art technology, now called 'Latent Fingerprint Identification,' it raised incriminating fingerprints from surfaces that couldn't be dusted for prints. Alvin Karpis, "Doc" Barker, Charles Fitzgerald, and the other members of the gang had gotten away, but they'd left their fingerprints behind—all over the ransom notes.
A Forensic First
It's called the Silver Nitrate Method and its application in the Hamm Kidnapping was the first time it was used successfully to extract latent prints from forensic evidence. Scientists had just thought to take advantage of the fact that unseen fingerprints contain perspiration, chock full of sodium chloride (common table salt). By painting the evidence, in this case the ransom notes, with a silver nitrate solution, the salty perspiration reacted chemically to form silver chloride—which is white and visible to the naked eye. There they were: hard evidence that the Karpis gang was behind the kidnapping. Case closed.
Today "latents" are developed by hugely sophisticated methods. The FBI's Latent Print Unit uses powders, lasers, and alternative light sources to detect and analyze partial and complete fingerprints. Its Cyanoacrylate process encloses evidence in a sealed cabinet and exposes it to cyanoacrylate glue fumes in order to bring up prints. Fluorescent lights and lens filters are also used to good effect. Then, once the latent print has been found, it is run through the Bureau's Integrated Automated Fingerprint Identification System (IAFIS)—an electronic network of databases of millions fingerprints, housed in the FBI's Criminal Justice Information Service Division in Clarksburg, West Virginia. When a match is made, chances are good that it's the beginning of the end of the investigation.