The Two William Wests
Around the turn of the 20th century, criminals arrested in certain jurisdictions were put through a kind of anthropometry, a series of facial, skull and bodily measurements intended to serve as identification. Fingerprinting hadn't yet caught on, and the version of this procedure pioneered by French police officer Alphonse Bertillonwas considered state-of-the-art.
So naturally, when the good people of New York sent Will West to Leavenworth prison, the record clerk followed procedure: He took West's measurements and sorted through the piled identification cards until one name remained: William West. This was bad news for Will, who claimed never to have had a previous run-in with the New York police. But there was his name, along with a set of nearly identical Bertillon measurements. Even the photograph on record was his spitting image [sources: Iowa Department of Public Safety, Olsen, Trimm].
Except it wasn't him. The William West on record, his near physical twin, was already in Leavenworth, serving a life sentence for murder. The discrepancy was soon resolved via fingerprints, and textbooks and speeches still cite the case as a classic example of the technique's usefulness. It's unclear what the consequences might have been for Will had the mistake not been caught; but at the very least, he likely would have received a harsher sentence for repeat offense [sources: Olsen, Trimm].