Common biological evidence includes which items?

• A. Blood
• B. Semen
• C. Saliva
• D. All of the above

Answer: (D)

Biological evidence in forensic investigations refers to bodily fluids or tissues that can be collected from a scene and analyzed to reveal DNA and other information. Blood, semen, and saliva are all common sources because they frequently transfer in various types of crimes and can yield individual DNA profiles. The best answer is all of the above, since each of these fluids is routinely encountered and analyzed as biological evidence. In practice, investigators use presumptive tests to quickly screen for a fluid type (for example, Kastle-Meyer testing for blood, acid phosphatase for semen, or amylase activity for saliva) and then follow up with confirmatory tests and DNA analysis to link people to scenes or objects. Understanding that these fluids are all commonly encountered helps explain why crime-scene evidence often includes multiple forms of biological material.