ABMDI Evidence Collection and Preservation 2 — Questions and Answers
Question 1: Why should biological evidence (blood, tissue) be collected into paper bags rather than plastic bags?
- Paper is lighter and easier to transport
- Plastic traps moisture, promoting bacterial growth that degrades DNA and may cause mold contamination (Correct answer)
- Paper bags are required by all state laws
- Plastic bags cause static discharge that can damage DNA
Correct answer: Plastic traps moisture, promoting bacterial growth that degrades DNA and may cause mold contamination
Moisture trapped in plastic promotes bacterial growth and can degrade biological evidence. Paper bags allow air circulation, preserving the integrity of biological samples.
Wet biological evidence (bloodstained clothing, tissue) sealed in plastic will mold and decompose rapidly, destroying DNA and contaminating the evidence. Paper bags allow moisture to dissipate. If wet evidence must be transported in plastic initially, it should be transferred to paper bags as soon as possible.
Question 2: What is the primary purpose of collecting a control sample at a death scene?
- To provide the crime lab with a backup in case the primary sample is lost
- To identify background contamination at the scene that might confound laboratory analysis (Correct answer)
- To establish the victim's identity before DNA analysis is completed
- To compare the decedent's DNA with the medical examiner's DNA
Correct answer: To identify background contamination at the scene that might confound laboratory analysis
Control samples (blank swabs or substrate controls) are collected to detect any pre-existing contamination at the scene that might affect the interpretation of evidence analysis.
A substrate control is collected by swabbing an unstained area near a biological stain to check whether the surface itself contains substances that might interfere with DNA analysis or other testing. If the control comes back positive, laboratory analysts know that the environmental substrate may affect results.
Question 3: When collecting bloodstain pattern evidence at a scene, the MDI should prioritize:
- Collecting all blood with swabs before photographing
- Thorough photography and documentation before any collection or disturbance (Correct answer)
- Painting over bloodstains to preserve them from environmental damage
- Immediate collection without documentation to prevent evidence degradation
Correct answer: Thorough photography and documentation before any collection or disturbance
Documentation through photography must occur before any collection begins to preserve the spatial and contextual information of bloodstain patterns.
Bloodstain pattern analysis (BPA) can reconstruct events at a scene including directionality, impact velocity, position of source, and movement. Photographing patterns in place (with and without scales) preserves this interpretive information. Only after thorough documentation should samples be collected for DNA analysis.
Question 4: Vitreous humor is frequently collected for toxicological analysis during death investigations because:
- It is the largest fluid compartment in the body
- It is relatively isolated and protected, making it less susceptible to redistribution and decomposition than blood (Correct answer)
- It contains higher drug concentrations than any other body fluid
- It is the only fluid that can detect alcohol consumption
Correct answer: It is relatively isolated and protected, making it less susceptible to redistribution and decomposition than blood
Vitreous humor is isolated in the eye and protected from postmortem redistribution of drugs, providing more reliable drug and alcohol concentrations than blood in advanced postmortem intervals.
Postmortem redistribution causes drug concentrations in blood to change significantly after death due to diffusion from tissues and the gut. Vitreous humor, being anatomically isolated, is largely immune to this effect. It is particularly valuable for ethanol analysis and electrolyte analysis (estimating postmortem interval).
Question 5: What is the appropriate way to package and preserve a firearm collected at a death scene?
- Immediately wipe down the firearm to preserve it from rust
- Document, render safe if loaded, photograph in place, then package in a paper bag with a label noting LOADED if applicable (Correct answer)
- Seal the firearm in an airtight plastic bag to preserve fingerprints
- Discharge remaining ammunition before packaging
Correct answer: Document, render safe if loaded, photograph in place, then package in a paper bag with a label noting LOADED if applicable
Firearms must be documented in place, safely rendered unloaded by qualified personnel, photographed, and packaged in paper bags with appropriate labels including loaded status.
Firearms collected as evidence must be handled according to safety protocols. Only qualified personnel should render them safe. The weapon's position, orientation, and distance from the decedent should be documented photographically before collection. Ammunition should be separately packaged. Paper packaging prevents moisture buildup.
Question 6: During scene investigation, the MDI identifies a substance suspected to be a controlled drug. What is the appropriate collection procedure?
- Test the substance using a field drug kit and discard the excess material
- Photograph the substance in place, collect using appropriate containers, seal and label with chain of custody, and submit to the laboratory (Correct answer)
- Contact the local pharmacy to identify the substance before collection
- Use bare hands to collect a sample, then seal in a plastic zip bag
Correct answer: Photograph the substance in place, collect using appropriate containers, seal and label with chain of custody, and submit to the laboratory
Suspected controlled substances must be photographed, properly collected with appropriate PPE, sealed in evidence containers, and submitted through formal chain-of-custody channels to the laboratory.
Suspected drug evidence must be handled with PPE due to potential fentanyl and other hazardous substance exposure. Collection should use appropriate containers (envelopes, vials) and the substance should be sealed, labeled, and logged into evidence. Field drug kits provide presumptive results only and should not substitute for laboratory confirmation.
ABMDI Evidence Collection and Preservation 2
Why should biological evidence (blood, tissue) be collected into paper bags rather than plastic bags?