Fingerprints are one of the best forms of physical evidence. A fingerprint can conclusively identify both offenders and victims.
Ask crime scene technicians to name the biggest problem that they encounter on the job and you will consistently hear the same response - crime scene contamination by curious officers, detectives, and supervisors.
Many criminal cases, even when investigated by the most experienced and best qualified investigators, are ultimately solved by an admission or confession from the person responsible for committing the crime.