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The smallest bit of evidence left at the scene of a crime can be used to identify and convict perpetrators. According to Wikipedia, the Locard Exchange Principle states:

“Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as a silent witness against him. Not only his fingerprints or his footprints, but his hair, the fibers from his clothes, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen he deposits or collects. All of these and more, bear mute witness against him. This is evidence that does not forget. It is not confused by the excitement of the moment. It is not absent because human witnesses are. It is factual evidence. Physical evidence cannot be wrong, it cannot perjure itself, it cannot be wholly absent. Only human failure to find it, study and understand it; can diminish its value. “    - Professor Edmond Locard

Criminals usually leave some form of trace evidence at the scene so it is left to crime investigators to find it. In the following case, profiled on Forensic Files (TRU tv), police were able to solve a case with only a shoe print.

A woman called 911, reporting someone breaking into her home.  The connection was broken and police rushed to the scene, arriving just minutes later.  The woman’s body was discovered on the bathroom floor; she had been shot in the head. 

There was little doubt of what had happened.  The woman heard the intruder, grabbed a cordless phone and hid in the bathroom.  The intruder kicked in the door, shot the victim and took her purse.  Police considered robbery to be the motive. 

Shards of glass were collected and sent to the lab in the hopes of find a shoe print.   The linoleum floor was dusted with a powder called Aurora Pink which will adhere to any moisture and fluoresce in UV light. Investigators did find a heel print on the floor and a toe print was discovered on the glass, using a technique called fuming, in which Super Glue is heated and the fumes adhere to print. 

SoleMate is a data base of shoe patterns used to identify specific brands and models of shoes.

Six weeks later a suspect was apprehended breaking into another home in the neighborhood.  His shoes were inked and printed.  Using transparent overlays, comparisons were made between the two impressions, using class characteristics and accidental characteristics.

Class characteristics are based on how the shoe is made, while accidental characteristics are those occur when the shoe is worn, such as patterns of wear or scratches.  The patterns of the suspect’s shoes and the prints recovered from the scene did not match.

Police found a second suspect through a tip and recovered shoes from his mother’s home which did match the evidence.  Upon questioning he confessed to the crime and pled guilty. 

Additional information about fuming

The super glue method was first employed by the Criminal Identification Division of the Japanese National Police Agency in 1978. 1

Cyanoacrylate (CA) is the adhesive used in Super Glue.  

There are three techniques for making latent fingerprints visible:  physical techniques, chemical techniques, and instrumental techniques. CA fuming is a chemical technique. 1

Fumes from warmed CA can develop latent fingerprints on smooth surfaces like glass, plastic, etc

Super glue reacts to traces of amino acids, fatty acids, and proteins transferred from fingertip to produce a visible, sticky white material that forms along the ridges of the fingerprint.  1

Usually the fingerprints are visible to the naked eye, but if not, a luminescent substance may be added and the print will be visible using UV light. 2

1. Brown, Eric W:  The Cyanoacrylate Fuming Method

2. Wikipedia: Cyanoacrylate