Criminal Investigations: Chapter 5 Study Notes

Criminal Investigations: Chapter 5 Study Notes

Objectives

  • Differentiate the types of DNA evidence.

  • Analyze the collection methods and best practices of evidence collection.

Opening Question

  • What is real evidence?

    • Real evidence is also known as physical evidence, scientific evidence, or forensic evidence.

    • It is powerful in a trial setting due to its objectivity and direct relation to the crime scene or the individuals involved.

DNA - The Basics

  • DNA (Deoxyribonucleic acid):

    • The genetic building block of all living organisms.

    • Exception: identical twins have identical DNA.

  • DNA Analysis:

    • Process of extracting DNA from cells, also referred to as typing or printing.

  • Buccal (oral) swab:

    • A sterile cotton swab used to swab the inside of an individual’s cheeks.

    • Utilized to collect DNA from a suspect for comparison or reference purposes.

Chain of Custody

  • Steps in the Chain of Custody:

    1. Collected the piece of evidence and initiate the chain of custody.

    2. Transported the evidence to the police department or crime lab.

    3. Logged the evidence into the evidence room.

    4. Received the evidence from the lab for final inventory.

Potential Problems and Limitations

  • Presence of a DNA match does not necessarily constitute absolute proof of guilt.

  • Alternative explanations for the presence of DNA may exist.

  • Indirect transfer (or secondary transfer) of DNA:

    • Occurs when DNA is transferred between objects or persons via another person or object.

Blood Evidence

  • Commonly found in violent crimes.

  • Luminol:

    • A chemical that helps detect areas where blood once was, which may not be visible to the naked eye.

  • Blood Spatter:

    • Patterns of blood resulting from a violent crime that can provide investigative insights.

  • Hidden Blood:

    • Blood that is not visible and may require special techniques to reveal.

Semen

  • Often found in sexual offenses.

  • Locations where semen may typically be found:

    • On the victim, on the victim’s clothing, inside condoms, and in places where the assault occurred.

  • Tests to identify the presence of semen:

    • Microscopic identification of spermatozoa.

    • Acid phosphatase test.

    • Detection of choline and p30.

    • Use of ultraviolet (UV) light or alternative light sources.

Saliva

  • Most likely found in the following areas:

    • On cigarette butts, bite marks, bottles and cans, chewing gum, clothing, envelopes, and stamps.

Hair

  • Commonly recovered in cases involving homicides, assaults, and hit-and-run incidents.

  • Important Collection Notes:

    • Prevent damage to the root of the hair.

    • At least 25-50 hairs should be collected for analysis.

Other DNA Evidence

  • Types:

    • Urine, feces, vomit, and perspiration can all be subjected to DNA analysis.

  • Touch DNA:

    • Also known as trace DNA or contact DNA.

    • Occurs when contact is made between the victim and the perpetrator; skin, blood, and/or hair may be recovered from under the fingernails of the victim.

  • Limitations:

    • Includes issues such as indirect transfer, contamination, and degradation of samples.

Crime Board Project

  • Instructions:

    • Choose a case and bring a poster board to the next class for presentation.

References

  • Brandl, S. G. (2025). Criminal investigation (6th ed.). SAGE Publications.