To Catch a Thief
Today, DNA is the gold standard for criminal evidence. But often there is no DNA at the scene of a crime. Then, old-fashioned fingerprint analysis may be used. A skilled analyst can identify an individual from a single good print because no two people have identical fingerprints. But you have to be able to see the prints to analyze them.
The Back Story
- Fingerprints are often present at a crime scene, but they may not be visible. These fingerprints are called latent prints.
- When people touch objects with their fingers, they may leave behind traces of skin oils. The oil soutline the pattern of whorls on their fingers.
- One method for bringing latent prints into view is called iodine fuming. Iodine is a halogen element in Group 17 of the periodic table. Iodine undergoes sublimation, and this is the basis of iodine fuming.
- You can see how iodine fuming is done and how it makes latent fingerprints visible by watching this video:
Show What You Know
Learn more about iodine fuming to reveal latent fingerprints at the link below. Then answer the questions that follow.
- In what state of matter does iodine occur at room temperature? What happens to iodine when it is heated?
- What chemicals in fingerprints interact with iodine vapor? What happens when this occurs?
- What is a fixative? How and why must a fixative be used on fingerprints revealed by iodine fuming?
- Why is it important to keep iodine crystals in a closed container, especially when heating them?
- Briefly describe another method of revealing latent fingerprints.