ABMDI Forensic Science Applications 2 — Questions and Answers
Question 1: Which of the following describes the principle of Locard's Exchange?
- Every person at a scene leaves something behind and takes something away (Correct answer)
- Forensic evidence must be independently verified by three experts
- DNA evidence always takes precedence over physical trace evidence
- Every crime scene must be documented by both law enforcement and the MDI
Correct answer: Every person at a scene leaves something behind and takes something away
Locard's Exchange Principle states that whenever two objects come into contact, there is a transfer of material between them. This is the foundational principle of trace evidence.
Edmond Locard's principle underpins all trace evidence collection: fibers, hair, glass, soil, pollen, paint transfer. At death scenes, this means the perpetrator may have left trace materials on the decedent or scene, and may have taken materials away. MDIs must preserve trace evidence by preventing unnecessary contact with the body and scene before evidence collection is complete.
Question 2: Forensic anthropology is most useful to an MDI investigation when:
- Toxicology results are needed quickly
- Skeletal or highly decomposed remains must be assessed for biological profile (age, sex, ancestry, stature) (Correct answer)
- The decedent's fingerprints need to be compared to AFIS
- Cause of death involves cardiac pathology
Correct answer: Skeletal or highly decomposed remains must be assessed for biological profile (age, sex, ancestry, stature)
Forensic anthropologists specialize in analyzing skeletal and highly decomposed remains to estimate biological profile and detect trauma.
Forensic anthropologists can estimate age at death (from epiphyseal fusion, dental wear, arthritic changes), sex (from pelvis and skull morphology), ancestry (from skeletal features), and stature (from long bone lengths). They can also identify perimortem trauma, which is critical for manner of death determination.
Question 3: In a suspected drowning death, which autopsy finding is commonly associated with drowning but is NOT pathognomonic (specific) for it?
- Lividity limited to the upper torso
- Pulmonary edema and water in the airways (Correct answer)
- Petechial hemorrhages of the sclera
- Absence of external trauma
Correct answer: Pulmonary edema and water in the airways
Pulmonary edema and water in the airways are common in drowning but can also occur in other causes of death. They are not diagnostic of drowning alone.
Classic drowning autopsy findings include overdistended lungs, foamy water in airways, cutis anserina (goose bumps), and water in the stomach. However, these findings can occur in congestive heart failure, drug-induced pulmonary edema, and other conditions. Scene investigation and circumstances are essential to the determination.
Question 4: What does stippling (tattooing) at a gunshot wound indicate about the firing distance?
- The shot was fired from a distance greater than 4 feet
- The shot was fired within an intermediate range (approximately 6 inches to 3-4 feet), close enough for unburned gunpowder to embed in skin (Correct answer)
- The weapon was a high-powered rifle
- The wound was self-inflicted
Correct answer: The shot was fired within an intermediate range (approximately 6 inches to 3-4 feet), close enough for unburned gunpowder to embed in skin
Stippling (powder tattooing) is caused by unburned or partially burned gunpowder particles embedding in the skin, which only occurs within intermediate range.
Firing range determination from gunshot wounds: contact wounds show searing, burning, and gas pattern; close range shows soot deposition; intermediate range shows stippling without heavy soot; distant wounds show the entrance wound only. Stippling cannot be wiped away because the particles are embedded in dermis.
Question 5: Which toxicological specimen is preferred for postmortem analysis to avoid postmortem redistribution artifacts?
- Central blood from the heart
- Peripheral blood from the femoral vein (Correct answer)
- Blood from the pulmonary vein
- Blood from the jugular vein
Correct answer: Peripheral blood from the femoral vein
Femoral vein (peripheral) blood is preferred because it is furthest from drug-rich tissues (gut, liver, lung), minimizing postmortem redistribution artifacts.
Postmortem redistribution (PMR) is the passive diffusion of drugs from concentrated tissue reservoirs (liver, gut, lung) into adjacent blood. Central blood (cardiac) is most affected by PMR. Peripheral blood from the femoral vein, furthest from major organ reservoirs, is least affected.
Question 6: Wound track analysis during autopsy helps the MDI and medical examiner to:
- Determine the exact time of death
- Establish the direction of bullet travel, range of fire, and potential weapon characteristics (Correct answer)
- Confirm the decedent's identity
- Determine whether the decedent was standing or seated at the time of injury
Correct answer: Establish the direction of bullet travel, range of fire, and potential weapon characteristics
Wound track analysis establishes bullet trajectory (direction of travel), which informs reconstruction of the shooting including relative positions of shooter and victim, range, and weapon type.
Wound track analysis includes identifying entrance and exit wounds, tracking the path through tissue layers, recovering projectiles, and determining trajectory angle. This information is combined with scene reconstruction to determine firing position and whether the wound could be self-inflicted.
ABMDI Forensic Science Applications 2
Which of the following describes the principle of Locard's Exchange?