Friday, November 27, 2009

Shoe Prints Make Good Impressions

by Andrea

Criminals think they’re clever by not leaving fingerprints, but they may neglect another area: shoe prints. Shoe prints—or footprints, as they’re usually called—are the most common impression left at or near a crime scene.

Stepping Up
Prints are found outside in dirt, mud, clay, and snow. In urban areas they’re left on the rooftops of apartment buildings. Sometimes they are found inside when the perpetrator tracks dirt into the house—or when they have walked through something like paint, dirt, or blood. If investigators can use footwear or tire tread evidence to show that a person was at the crime scene, the suspect will have to have a good explanation for being there. If the impression found is created from blood, the suspect will need a really good explanation!

Comparisons: Start with Characterizing
Since shoe types and styles number in the thousands, comparisons are first narrowed down by size, type, brand, design, and shape. Then individual characteristics are studied such as nicks, cuts, or wear patterns. Perhaps a stone wedged into the tread. Even with flat-bottomed deck shoes, the stitching in soles is unique, and no two will look alike in a print.
When footwear impressions or tire tracks are found at a crime scene, they’re photographed. If a depression is left in mud, for example, a cast or moulage (French for casting/moulding) is made.

How to Make a Plaster Cast
Some special equipment is needed to make a perfect plaster cast. Here’s how the pros do it:
  •  Clean out any loose material without disturbing the impression. 
  •  Spray a fixative onto the surface.
  •  Build a portable frame or wood ledge and place it around the track mark.
  •  Mix plaster of Paris or dental stone casting material and pour it over the marks.  Another product, Snow Print Wax, can be used for impressions found in packed snow.
  •  Place reinforcement sticks or cheesecloth into the mixture.
  •  When casting is hard, carefully lift it out and put it in a cardboard box upside down to dry.
Gait Patterns, Too
Casts are used for identification, and they also provide clues to the movement, direction, and speed of the person who made them. For instance, the cast of a runner’s footprint will differ from that of a walker—a running foot will sink deeper in front, with less weight distributed to the heel upon landing. Analysts can also answer such questions as: Was he was carrying something heavy? Was he wounded? Did he carry soil away on his shoes as he left? (Soil samples are usually taken in case they are needed later, to match such soil.)
Latents (Not Readily Visible)

Latent shoe prints are found on counter tops, staircases, and walls, and footwear impressions can be lifted just like fingerprints using chemicals and powder. One bank robber climbed over the counter during a holdup—and his shoes matched the print made on the surface perfectly.

But for the flimsiest of all evidence, shoe prints found in dust, another system is needed. The best way is to turn out the lights and shine a light—a flashlight will do—against the hard, dusty surface and document that with a photograph. In order to preserve these footprints, analysts use an electrostatic dust lifter. A sheet of black lifting material, like foil, is laid over the surface. A high-voltage charge is run through the material. The electricity makes the dust stick to the sheer, and voilà—an image! The process is nondestructive and works on just about any surface.

Unusual Prints: A Case Story
A state trooper in Alaska was called in to investigate several cases of moose poaching. (Bet you didn’t know that moose poaching is a crime.) Some earlier cases had been solved due to the carelessness of the criminals, who had left behind incriminating evidence such as a boot print and, in one memorable case, a wallet complete with the poacher’s driver’s license! One culprit, though, seemed to have left no clues at all—until police discovered a clear print of his license-plate number where he had backed his vehicle up against a snow bank. 

Photo courtesy of ©Ron Roberts 

 Excerpt from Andrea's Detective Notebook: Crime Scene Science (available on CD)


FleaStiff said...

I've heard tales of criminals wearing shoes that are markedly different than their own so as to leave prints that are either much larger or smaller than they would wear. I don't know how true these tales are or if someone attaching a smaller sole to the bottom of his shoe would be detected anyway.

Laura Cross said...

Great post Andrea! Very informative. I'm wondering if you know of any cases where the criminals attempted to "disguise" their footprints/shoe prints by wearing medical bootie shoe covers? I'm curious to know if that would be an effective method for eliminating a verifiable shoe print or if the imprint of the shoe would still come through, since the bootie is made of flimsy material?

piper said...

Just another head-shaker for the OJ case -- where he murdered two people. The shoe print matched but still they acquit.

FleaStiff said...

I do not recall any matching shoe print in the OJ case and would surely suggest great concern over the use of the word match, however, I doubt any shoeprint evidence will overcome a dumb jury with book royalties on their minds.

Johnnie K said...

Dear Ms Campbell. I am a criminal barrister from New Zealand. I greatly enjoyed and appreciated your superb research. It is extremely useful to me. I have a question: how would I find out how many different soleprints Converse produces? The issue has come u[ in a recent case and I have know of no way of finding out. Thank you for your research and assistance: John Kovacevich from Aukland New Zealand.