Who will be on the crime scene when a firearm is involved?
Lead firearms examiner – highly experienced and demonstrably competent
How do you make a gun safe?
- Must document and note the location and status of gun prior to handling it
- Note if the gun is cocked
- The position of any safety catch or mode of fire selector
- Note whether or not the gun is loaded
If no bullet is found at the scene what should be done?
close examination of damage and two simple
chemical spot tests can help
* During examination, you should record position and size of damage
* Spot test for lead and copper
What will appearance of bullet damage depend upon?
- The substrate material
- Shape, composition, velocity, and orientation of bullet relative to substrate
What can the shape of bullet damage determine?
Indicate the angle of impact
What can the position of cartridge cases do?
- determine where the shooter was
- number of cases grouped together can determine position of self-loading firearm
What can a forensic firearms examiners assist a pathologist with?
- What was the gun used?
- How far away was it from the victim when it was
discharged? - What are entrance and exit wounds?
- Based on relative position of entrance/exit wounds, it
may be possible to position the shooter relative to the
victim
What can shot gun discharge damage determine?
Shotgun shells contain multiple pellets. At close range (<1 m) the pellets can act as a single projectile, but
further than that and they start to disperse. Size of pattern may help in determining distance
What should not be submitted to the labratory?
A loaded firearm
Once the firearm had been made safe, what happens?
- Photographs are taken
- Note the nature and positions of any foreign material adhering to it
- Note a full description of make, model, and type of firearm
- Note the overall length, barrel length, and magazine capacity
What is Microscopic examination of breech and bore?
Note direction of twist and the number of lands and grooves
6. Bore wipe taken with filter paper or swab to collect gun shot residue (GSR)
7. Note position and nature of any markings or stamps (including serial numbers)
8. If serial number is hidden or obliterated, etching techniques might help visualize
How do we access if a firearm went of “by accident”?
- Must determine if the safety catches and mechanisms are working
- Must determine the force required to pull the trigger
- A series of drop and impact
tests may be performed to see
whether or not the firearm is
prone to accidental discharge
How do you determine if a gun is safe to fire? (which is a key issue that needs to be addressed)
- Important when dealing with modified, converted, or improvised firearms
- If unsafe, consider firing a primed cartridge case (with no bullet)
- Always use a remote test firing device
How do you test fire?
- Should be tested using a range of ammunition with different bullet and primer materials
- Undistorted bullets can be
recovered by firing into a water tank or box containing cotton wool or bespoke fibrous materials - Recovered bullets and cartridge cases should be placed in appropriately labelled bags
How do you measure bullet velocity to access lethality?
- A bullet chronograph is used to measure
velocity - The modern chronograph consists of two sensing areas called chronograph screens, which contain optical sensors that detect the passage of the bullet
- The bullet is fired so it passes through both screens, and the time it takes the bullet to travel the distance between the screens is measured electronically
How do you assess wound potential from a firearm?
- Comparative penetration tests can be conducted on ballistic gel
- How far do the projectiles
penetrate? - Compare a gun submitted to the lab with a known gun that is just capable of causing a lethal injury
- This kind of study can help
classify things as ‘deadly
weapons’
How do you determine the distance potential of a firearm?
- Test a firearm at various ranges
- Duplicate soot, propellant, or shotgun pellet pattern observed at the scene, at post-mortem examination, or on recovered clothing
- Sometimes exact replication is impossible and estimates have to be made
What can be done with ammunition to help solve the crime?
- Test a firearm at various ranges
- Duplicate soot, propellant, or shotgun pellet pattern observed at the scene, at post-mortem examination, or on recovered clothing
- Sometimes exact replication is impossible and estimates have to be made
What trace evidence can be found through ammunition?
- Helps determine what the bullet may have struck
- Damage on the sides can indicate a ricochet – can
find the angle of impact by looking at the bullet - Cartridge case marks are noted and assessed
- Shape
- Position of the ejector and extractor
- Firing pin impression
- Breech face
- Chamber marks
What is comparison microscopy?
Two microscopes joined by an optical bridge – uses a prism to enable two
objects to be viewed simultaneously, side by side, at the same magnification
