CSI - Crime Scene Investigator Biological and Trace Evidence Questions and Answers

Question 1

An investigator uses a luminol-based test on a carpet at a homicide scene, which results in a positive reaction indicating the possible presence of blood. Which of the following statements is most accurate regarding this result?

Accepted Answer

The test is a presumptive test and only suggests that blood might be present, requiring further confirmatory testing.

Answer

Luminol is a classic example of a presumptive (or screening) test. It is highly sensitive to the presence of hemoglobin but can produce false positives with other substances like bleach, certain metals, and plant peroxidases. Therefore, a positive result only indicates the possibility of blood, and a more specific confirmatory test, such as RSID or immunological tests, must be performed to confirm its presence and origin.

Question 2

At a scene, a CSI finds several loose, dark fibers on a light-colored couch near the victim. Which of the following is the most appropriate method for collecting these fibers to prevent loss and contamination?

Accepted Answer

Using clean forceps to pick up individual fibers and placing them into a folded paper bindle, which is then placed in a labeled envelope.

Answer

The preferred method for collecting visible trace evidence like fibers is to use clean forceps or tweezers to handle them individually. This prevents contamination and preserves their integrity. The fibers should then be placed into a paper bindle (also known as a druggist's fold), which keeps the tiny evidence secure. This bindle is then placed into a properly sealed and labeled envelope or other container. Using tape can be destructive, and brushing or vacuuming a large area risks cross-contamination and loss of context.

Question 3

A forensic lab receives a small, degraded bone fragment from a decades-old cold case. Investigators hope to link the remains to a maternal relative of the suspected victim. Which type of DNA analysis would be most suitable and likely to yield a result?

Accepted Answer

Mitochondrial DNA (mtDNA) analysis.

Answer

Mitochondrial DNA (mtDNA) is ideal for this scenario for two key reasons. First, mtDNA exists in much higher copy numbers per cell compared to nuclear DNA, increasing the chance of obtaining a viable profile from small or degraded samples like old bone. Second, mtDNA is inherited maternally, meaning an individual's mtDNA sequence is the same as their mother, siblings, and other relatives along the maternal line, making it perfect for establishing a link to a maternal relative.

Question 4

An officer is collecting a Gunshot Residue (GSR) kit from the hands of a suspect who was apprehended three hours after a shooting. What is the correct procedure for using the SEM stubs for collection?

Accepted Answer

Use a dabbing or pressing motion to sample the web area between the thumb and index finger, as well as the palms.

Answer

The proper technique for collecting GSR with a scanning electron microscope (SEM) stub is to use a dabbing or pressing motion, not rubbing. This ensures the microscopic particles adhere to the stub's surface. Key areas to sample are the back of the hand, especially the web area between the thumb and forefinger, and the palm. Each hand should be sampled with a separate, clearly labeled stub.

Question 5

Which of the following pieces of trace evidence should be packaged in an airtight container to prevent its degradation or loss?

Accepted Answer

A piece of charred wood flooring suspected of containing an accelerant.

Answer

Evidence from a suspected arson scene, such as charred material that may contain a volatile accelerant (e.g., gasoline), must be packaged in an airtight container like an unlined metal paint can or a glass jar. This prevents the volatile chemical compounds from evaporating before they can be analyzed at the laboratory. Biological evidence like wet bloodstains should be air-dried and packaged in paper to prevent mold and bacterial growth, while other dry trace evidence is typically packaged in paper bindles or vials.

(CSI) Crime Scene Investigator Practice Test

(CSI) Crime Scene Investigator Practice Test

CSI - Crime Scene Investigator Biological and Trace Evidence Questions and Answers