Illinois Law Enforcement Training and Standards Board (ILETSB) Practice Exam

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Study for the Illinois Law Enforcement Training and Standards Board Exam. Prepare with flashcards and multiple choice questions, each with detailed explanations. Ace your exam and advance your career with confidence!

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What substance creates a latent fingerprint on skin ridges?

Water-based oil solution
Ink residue
Blood
Alcohol

The correct answer is: Water-based oil solution

The correct answer is a water-based oil solution because latent fingerprints are typically formed from the natural oils and moisture present on a person's skin. When a person's fingers come into contact with a surface, these oils can leave an impression or mark that is often invisible to the naked eye. This oil solution can include sebum—a substance produced by sebaceous glands in the skin—mixed with sweat and other contaminants. Other substances listed do not naturally create latent fingerprints in the same way. Ink residue is typically deposited when a person writes or marks something, and while it can leave a visible print, it does not represent the body's natural oils. Blood can leave a mark but is a different type of biological evidence, not a latent fingerprint from skin oils. Alcohol may evaporate quickly and does not play a role in the formation of latent prints on the skin. Thus, the water-based oil solution is the most accurate representation of the substances required for latent fingerprint formation.