Firearms and Toolmarks FA4

What are toolmarks in forensic science?

Markings created on a softer surface by contact with a tool

What are striated toolmarks?

Marks produced by lateral force and motion

What are impressed toolmarks?

Marks produced when a tool applies compressive force

Where are toolmarks commonly found?

At burglary scenes involving forcible entry

What are class characteristics of toolmarks?

General features like the size and shape of the tool

What are sub-class characteristics of toolmarks?

Irregularities from the manufacturing process

What are individual characteristics of toolmarks?

Unique marks from random nicks or breaks due to tool use

Why is it difficult to duplicate a toolmark in the lab?

Because of the unique and random nature of individual characteristics and contact angles

What steps are taken when collecting toolmark evidence?

Photograph with scale

What does “compare like with like” mean in toolmark analysis?

Only compare similar types of toolmarks under similar conditions

What is 3D imaging used for in toolmark analysis?

Provide x, y, and z coordinates of microscopic features

What is the purpose of a presumptive test for GSR?

To suggest the possible presence of GSR but not confirm it definitively

What is the purpose of a confirmatory test for GSR?

To definitively confirm the presence of GSR using more specific and reliable methods

What is an example of a presumptive test for GSR?

Sodium rhodizonate test (tests for presence of lead)

What is an example of a confirmatory test for GSR?

SEM-EDX (Scanning Electron Microscopy with Energy Dispersive X-Ray)

What is bullet wipe?

A dark ring around a bullet hole

How is gunpowder residue used in firearm analysis?

To determine the distance from which a weapon was fired based on residue distribution

At what distance does gunpowder residue usually no longer deposit on targets?

Beyond 3 feet (91.4 cm)

What can the sodium rhodizonate (NaRh) test detect on dark-colored fabrics?

It can confirm bullet entry and determine close-range firing

What does a visible residue pattern on clothing suggest about firing distance?

That the shot was fired at close range

What can infrared photography be used for in GSR analysis?

To reveal residue patterns on dark or patterned clothing

How does primer residue reach a shooter’s hands?

It is blown back toward the shooter when a firearm is discharged

What elements are commonly measured in primer residue analysis?

Barium and antimony (and often lead)

Where on the hand is GSR typically sampled?

Thumb web

What are major elements found in primer residues?

Lead

What are some minor elements in primer residue?

Aluminum

What is the typical size of GSR particles?

0.1–10 micrometers (μm)

What is SEM-EDX used for in GSR analysis?

To examine particle shape and elemental composition using automated analysis

What are possible conclusions from GSR examination?

The subject discharged a firearm

What limits the application of GSR analysis?

Risk of contamination and inability to definitively prove who fired the weapon