QUESTION IMAGE
Question
empty shell casings were found at two different crime scenes during the last month. they are labeled a through l. police test-fired firearms belonging to the suspects and compared firing pin impression marks made by those found on crime-scene casings.
procedure:
- view each shell casing with a hand lens or stereo microscope to determine each of the following: the caliber, headstamp, location of firing pin strike (center or rim), and description of firing pin marks. record your data on the data table below. point values for each section are in parenthesis.
cartridge shell casings made from test firing guns from the three suspects.
data table: comparison of casings (20 points)
| suspect 1 | suspect 2 | suspect 3 | |
|---|---|---|---|
| headstamp marking | |||
| firing pin strike (center or rim) | |||
| description of mark |
evidence cartridge shell casings recovered from previous robberies.
- using the three cartridge casings from the three suspects and your information from data table 1 above, determine if any of the crime-scene casings match casings from the suspects. if so, write the suspect # on the appropriate lines below. (20 points)
final analysis:
- of the three suspects, which one(s) could you link to the crimes? (10 points)
- based on the shell-casing matches, which of the three suspects could not be linked? (10 points)
- describe specific (unique) characteristics that linked one of the suspects casings to the crime-scene casings.
Step1: Record suspect casing data
| Suspect 1 | Suspect 2 | Suspect 3 | |
|---|---|---|---|
| Headstamp marking | FEDERAL .40 S&W | FEDERAL .40 S&W | FEDERAL .40 S&W |
| Firing pin strike (center or rim) | Center | Center | Center |
| Description of mark | Circular with a small inner notch at 6 o'clock | Circular with a pointed inner indent at the top | Circular with a wide, flat inner indent at the top |
Step2: Match crime scene casings
- A: Matches Suspect 1
- B: Matches Suspect 1
- C: Matches Suspect 3
- D: Matches Suspect 2
- E: Matches Suspect 3
- F: Matches Suspect 2
- G: Matches Suspect 1
- H: Matches Suspect 3
- I: Matches Suspect 2
- J: Matches Suspect 3
- K: Matches Suspect 2
- L: Matches Suspect 3
Step3: Analyze linked suspects
All 3 suspects have matching casings.
Step4: Analyze unlinked suspects
No suspects lack matching casings.
Step5: Identify unique characteristics
Suspect 1's mark has a 6 o'clock notch.
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Completed Data Table:
| Suspect 1 | Suspect 2 | Suspect 3 | |
|---|---|---|---|
| Headstamp marking | FEDERAL .40 S&W | FEDERAL .40 S&W | FEDERAL .40 S&W |
| Firing pin strike (center or rim) | Center | Center | Center |
| Description of mark | Circular, 6 o'clock inner notch | Circular, pointed top indent | Circular, wide flat top indent |
Crime Scene Casing Matches:
- A: #1
- B: #1
- C: #3
- D: #2
- E: #3
- F: #2
- G: #1
- H: #3
- I: #2
- J: #3
- K: #2
- L: #3
Final Analysis:
- Suspect 1, Suspect 2, and Suspect 3 can all be linked to the crimes.
- None of the three suspects could be ruled out (all have matching casings from crime scenes).
- Suspect 1's test-fired casings have a unique small notch at the 6 o'clock position on the firing pin mark, which matches the identical notch present on crime scene casings A, B, and G.