Fingerprints

6.  In 1863, French Professor Paul-Jean Coulier from Paris wrote a paper explaining that latent fingerprints can be developed by iodine fuming.  He also explained how to fix these prints once he'd developed them. 

10.  Juan Vucetich, an Argentinean police official, made the first criminal identification of Francisca Rojas in 1892.  

By 1897, two Indian fingerprint experts, Azizul Haque and Hem Chandra Bose developed the Henry System of fingerprint classification.  This system continued to be used until records were computerised.  Then after an enquiry into their use, The Fingerprint Branch of the Metropolitan Police in London was established in July 1901. 

In 1903, in New York, it became practice for criminals' fingerprints to be taken. Gradually, this practice started to spread across the US, not just for criminal identification but also for service personnel and those employed in law enforcement.  (It is still common practice for UK police officers to have their fingerprints taken on joining the police service, so that they are readily available for elimination purposes at crime scenes.  Although crime scene management is more sophisticated nowadays, prints can be left through latex gloves, so elimination is important.)

Nowadays, collecting fingerprint evidence is a common part of crime investigation.  Prints are classified into one of three types: Latent, Patent or Impressed. 

Latent prints are those that are not visible to the naked eye.  They can be made visible by chemical treatment.

Patent prints are clearly visible to the naked eye, usually because the owner of them has put their fingers in something like blood or some other substance. 

Impressed prints (where an impression has been made) are those where the fingers have been pressed into some sort of soft material.  Sometimes, a cast can be made of these.

Even partial prints can be used as reliable evidence, and nowadays, computers do the work that the fingerprint officers used to do - comparing different sets of prints to find a match, which increases the accuracy even more.