By the 1900s what type of evidence was being collected at crime scenes to positively identify suspects by one particularly unique trait

By 1900, Fingerprint was the evidence which was collected at crime scenes to help positively identify suspects by one particularly unique trait.  No two people can have the same type of fingerprints. It is a unique characteristic which is even not common among identical twins. Therefore, was considered as an important evidence for identification of suspects and linking them with the scene of offence. In 1904, the city of St.Louis, Missouri used fingerprint evidence for the first time for criminal identification.

i believe the answer is snake.