SkillsUSA Crime Scene Practice Test 2026 - Free Crime Scene Investigation Practice Questions and Study Guide

Blood and semen are considered rich sources of DNA evidence because they contain a high concentration of nucleated cells, which hold the genetic material necessary for DNA analysis. Blood is especially valuable because it is widely encountered in crime scenes and can provide a robust profile of an individual, assuming the sample is not degraded. Semen, typically collected from sexual assault cases, also contains sperm cells that are particularly rich in DNA. The process of isolating DNA from these sources is well-established and reliable, making them excellent choices for forensic investigations.

In contrast, hair fibers typically do not contain nuclear DNA unless the root is present since hair shafts are made of keratin and do not have cells. Skin cells can yield DNA but typically in much smaller amounts unless there is enough cellular material collected at a scene. Body odor does not provide DNA; it consists of volatile compounds that can be indicative of a person but do not contain genetic information suitable for analysis.