Almost everything about human appearance changes or could be changed, except for fingerprints. Criminals in centuries past escaped by adopting disguises, adding or subtracting weight, hair or a myriad of other factors; but barring serious accidents or diseases like leprosy, the fingerprints one is born with are the fingerprints one keeps. That permanence, combined with the uniqueness of the print – no two were ever found alike among the billions now on record – made it the perfect law enforcement tool.

On this day, March 27, in 1905, fingerprint evidence from taken from the cash box of a murder scene in South London, England, led to the arrest of the killer. A tip led police the to Alfred Stratton and his brother, and Alfred’s girlfriend told the police interviewer he acted strangely the day after the murder. Sure enough, Alfred’s thumb matched the print from the crime scene.

Before fingerprint forensics became de rigeur, a commonplace technique for identifying criminals came from a French anthropologist Alphonse Bertillon. His system, later pared down to a formula, involved the precise measurements of arms, legs, facial features and body parts. That worked well enough, until the arrest of a William West — it turned out the Leavenworth Prison, where he was assigned, already had a Will West, and Will by formula had the exact same numbers as William. The two men were discovered to be identical brothers, and had been in frequent correspondence with each other. Fingerprint identifications were able to tell the two apart anyway.