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Questions and Answers
What is the primary focus of the Impression Section examiners?
Which type of impression can be analyzed as a three-dimensional impression?
What is NOT one of the purposes of examining impression evidence?
What must be considered when making a positive identification between the source and impression?
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Which conclusion can an examiner potentially reach from analyzing impression evidence?
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Why is quick recovery of impression sources important?
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What type of prints are categorized as two-dimensional impressions?
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What elements are evaluated to identify a specific tire or footwear item?
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What should be done to minimize ambient light when photographing impressions?
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What is the purpose of taking photos with different aperture settings?
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How many feet of circumference should be documented for tire impressions?
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What should be used to enhance contrast in snow impressions?
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Which flash settings are recommended when photographing impressions?
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What type of camera is recommended for photographing three-dimensional impressions?
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What is the preferred image format for capturing evidence photographs?
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What should be avoided when using primer spray paint on snow impressions?
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Why is it important to ensure the scale is at the same depth as the impression?
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Why is it important to photograph impressions at a 1:1 ratio?
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What is a common technique to ensure continuity when taking multiple photos of an impression?
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What should be included in the examination quality photographs alongside the impression?
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How should the camera be positioned when photographing the impression?
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What is the recommended positioning of the measuring scale in relation to the impression?
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Why should impression evidence be prioritized for early consideration?
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What angle is recommended for holding the flash when photographing impressions?
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What type of scale is preferably used for impressions?
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What is recommended to practice before collecting evidence impressions?
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What should be done with moist or damp impressions when collecting evidence?
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What type of media is preferred for submitting images of impressions?
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How should shoes and tires be packaged for evidence submission?
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What should you avoid using to package the dust lift on EDPL film?
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Which method is NOT suitable for recovering powder developed impressions?
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What characteristic of Stat-LiftTM is important for its function?
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What should you do after lifting an impression with tape?
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Which tool is specifically mentioned as effective for lifting dust impressions?
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What does dental stone do when applied to visible residue impressions?
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What type of materials can dental stone successfully recover impressions from?
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What is the advantage of using wider fingerprint tape for lifting impressions?
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Study Notes
Impression Evidence
- Impression evidence can include shoe or tire impressions in a variety of mediums.
- Three-dimensional impressions occur in materials like soil, snow, sand, and mud.
- Two-dimensional impressions are found on solid surfaces, such as floors, counters, car hoods, and paper
- Examination aims to determine if there are discernible characteristics for comparison
- Examinations can identify make, design, physical size, wear/manufacturing characteristics, and randomly acquired features
- Comparison of questioned impressions with a known object can determine if the object made the impression.
- Possible conclusions include identification, exclusion, or various levels of association.
Collection Guidelines
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Three-Dimensional Impressions (e.g., in soil)
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Method I - Photographic Documentation
- Use a digital SLR camera with the ability to attach an off-camera flash.
- Take photos in the camera's RAW format and convert to TIFF for laboratory submission.
- Use the highest megapixel camera available to achieve 300PPI resolution at size (1:1).
- Photograph impressions using a tripod and aligning the sensor plane directly over the impression.
- Step 6: Include a scale alongside the impression containing identification information. Bury the ruler to approximately the same depth as the impression.
- Step 7: Use low oblique lighting with the flash held approximately three feet from the impression. Photograph at 10°, 30°, and 45° angles to highlight the impression.
- Step 8: Bracket the series of photos, photographing at various aperture settings, such as f8, f11, and f16.
- Step 9: For tire impressions, ensure the entire circumference is documented with overlapping photos.
- Step 10: Lightly sprinkle black fingerprint powder onto snow impressions for contrast. Use black or gray primer paint for highlight purposes.
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Method II - EDPL Lifting
- Not recommended for moist or damp impressions. Practice lifting techniques prior to evidence collection.
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Method III - Lifts
- Gel Lifters are latex with a bonded adhesive layer suitable for lifting and preserving dust impressions.
- Stat-LiftTM is a statically charged film that’s commercially available for lifting dust impressions.
- Wide fingerprint tape is a viable option for two-dimensional impressions. Dust impressions with fingerprint powder before lifting.
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Method IV - Dental Stone Casting
- Best for visible residue impressions. Dental stone absorbs residue material and cleans the surface.
- Cast in the same manner prescribed for three-dimensional impressions.
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Submission Reminders
- Prioritize evidence by searching for it at the approach, entry/exit ways, path through the scene, escape route, near other impressions, and on floors, walls, doors, and the roof. Protect impressions from contamination.
- Practice new techniques on test impressions before working with evidence.
- Use the correct method based on the type and condition of the impression.
- Submit images on a CD or DVD in TIFF format.
- Package shoes in paper bags and each tire separately.
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Description
Explore the key concepts of impression evidence, including shoe and tire impressions in different materials. Learn about the characteristics examined during forensic analysis and the methods for collecting three-dimensional impressions. This quiz will test your understanding of the identification and comparison process in forensic science.