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Fingerprint Identification (Crime Fighters: Station 2)

In this activity, the student detectives will compare the evidence to fingerprint samples provided by each suspect. The collection of fingerprints at a crime scene is a very important task for forensic scientists because fingerprints reveal who might have touched what.

There are two types of fingerprints:

  • direct print (where the finger creates a visible impression in an object or substance)
  • latent print (where the finger leaves an invisible mark)

Latent fingerprints are created by dirt, sweat, or other residue left on another object. Forensic scientists can “develop” latent fingerprints to make them visible by dusting for them or by using a chemical method called fuming.

Fingerprints have three main classes structures: the arch, whorl and loop.

  • Arches have lines that start on one side and rise and exit on the other side of the print. They look like a hill.
  • Loops have lines that enter and exit on the same side of the print. They look like an upside-down U.
  • Whorls have circles that spiral and do not exit on either side of the print. They look like a bull’s eye.

Every fingerprint is unique, but there are certain patterns that can be observed which many prints have in common. Interestingly, even fingerprints from the same individual can vary slightly from finger to finger!

Baring loss of a finger tip to injury, or intensive scarring, the fingeprint patterns of individuals will constantly re-grow the same way as their skin re-news throughout their lives

Premise: Latent Fingerprints in the Kitchen
Entering into the Grizzly family’s kitchen, police noticed that many dishes had been used, perhaps by the suspect. Police bagged several dirty bowls and drinking glasses to dust for fingerprints. These were sent to the lab to be processed. 

Can your student detectives identify who left what print where?

Objectives

  • Carefully compare, analyze and record evidence (fingerprints) to infer a likely suspect.

Materials

  • Per Student:
    1 Crime Fighter’s Case Book
    pencil

  • Per Station:
    bowls and drinking glasses with latent fingerprints
    charcoal dust or cocoa powder
    soft brushes
    1 set of fingerprints per suspect (3 total)
    pair of first-aid gloves

Key Questions

  • What are latent fingerprints?
  • What types of patterns do you see?
  • How closely do the patterns you see in the evidence match the patterns provided by the suspects?
  • Is one person’s fingerprint the same across all of their fingers?
  • How do you know which finger’s print you are looking at on the evidence?

What To Do

Preparation

  1. Create three sets of Fingerprint Identification Cards, one for each volunteer suspect (including the volunteer culprit- often it is a good idea that this be the Teacher)
  2. Have the culprit create a latent fingerprint on each of the kitchen items you’ll be providing as evidence. To create a latent print, rub one of finger along the side of your nose to make it oily and then press the fingertip to the side of the glass or bowl. (Oily or sticky fingers leave the best prints.)
  3. Load the brush with charcoal powder and then gently brush the powder onto the side of the glass so that the fingerprint is coated.

Teacher Tip: Using too much powder can result in a smudged print. Instead of putting the brush directly into the powder, shake the closed jar then load the brush using only the powder that has transferred to the lid of the jar.

  1. Use the brush to gently sweep away the excess powder to reveal the print (where the powder has stuck to the oils left behind by the finger ridges).
  2. Present the cups and bowls as evidence. Provide gloves so that the detectives can work without compromising the evidence.

Activity

  1. Using the fingerprint pattern chart, students identify the type and characteristics of the prints found on the glasses and bowl.
  2. Detectives compare the prints on the dishes to a set of inked fingerprint cards provided by each suspect and determine which best matches the evidence.

Optional
Set up the station so that the student detectives process the fingerprints themselves. In this case, provide many samples of prints, so that all students can participate. Alternately, use the superglue fuming technique. See Fingerprint Fuming for more details on how to develop prints using the dusting and fuming methods.

Other Resources

Science World | Fingerprint Patterns PDF