Shooting Scene Investigation Notes - lect 8
Shooting Scene Investigation
Introduction
The first ranges of topics are in preparation for lab sessions in the second half of the term.
The labs will cover aerodynamic effects and air resistance.
Shooting scene investigations involve a vast range of analyses.
The investigation is often referred to as a shooting reconstruction.
Reconstruction vs. Reenactment
Reconstruction:
Science-based.
Utilizes information from:
Physical evidence at the scene.
Analyses of physical evidence.
Inferences drawn from analyses.
Aims to test various theories of prior events.
Involves collecting physical evidence from the scene (or potentially across a wider area if a firearm has been moved).
Seeks to create an accurate picture of the shooting event.
Acknowledges that multiple possibilities may exist due to:
Dynamic scenes (people move).
Limitations in the specificity of evidence analysis - evidence can't always tell us exactly to the millimeter where everything was and how it all came together.
Presents a range of possible solutions based on evidence, such as:
Possible locations of the shooter.
Positions of individuals at the time of the shooting.
Considerations of movement before or after the shooting/death.
Factors to consider:
Overlapping evidence.
Movement of evidence.
Transfer of evidence from one scene to another (e.g., gunshot residue).
Secondary transfer of evidence.
The ballistic expert presents ballistics information as one piece of a larger puzzle.
Other forensic evidence (fingerprints, DNA) contributes to a more accurate picture.
The police investigation is separate from forensic analysts.
Reenactment:
Less science-based.
Demonstration based on conjecture rather than scientific principles.
May involve unreliable eyewitness accounts.
Can be useful to test reconstructions, but scientific validity is paramount.
Objectives of Shooting Reconstruction
Assist the criminal justice system in solving crimes.
Answer key questions:
Who was involved?
What happened?
When did it happen?
Where did it happen?
How did it happen?
Why did it happen?
Understand component factors:
Trajectories (external ballistics).
Distances (close range, contact, long range).
Cartridge cases.
Bullet ricochet.
Effects of bullets passing through various materials.
Corroborate or dismiss claims made about the shooting in court.
Help the legal and policing systems ensure the right person is held accountable.
Initial Questions
Was it a shooting in the first place?
Is there definitive evidence that a firearm was used?
A bullet hole alone is insufficient without attributing it to a bullet.
Good evidence: Bullet embedded in a wall or recovered from a body.
Consider alternative causes of holes (drills, crossbows, etc.).
Criminals are often well-informed and attempt to avoid leaving forensic evidence.
Do not assume a shooting based solely on hearing a loud bang.
Bullet Scenarios
Four main scenarios:
Perforation: Bullet passes through the target, creating entry and exit holes.
Penetration: Bullet enters the target but does not exit (entry, no exit).
Fragmentation: Bullet breaks up, with fragments either retained or passing through (mixture of penetration and perforation).
Ricochet/Bounce: Bullet bounces off the surface, either intact or fragmented.
Different ammunition types behave differently upon impact (some designed to break up, others to mushroom).
Body armor is designed to spread energy over a wider area, reducing penetration.
Analyzing Bullet Holes
Start with where the bullet ends up and work backwards.
Follow the trajectory backwards from the exit wound (if present) to the potential location of the firearm.
Indications of firearm use:
Bullets.
Cartridges.
Fragments.
Gunshot residue deposits (only at close range and requires confirmation tests).
White ring around entry holes.
Size and shape of the hole.
Evidence of high-energy penetration and damage localized to the hole.
()Gunshot residue is only useful for close range, usually, up to a few meters or so. The particles are so small that they don't have huge mass and as we've already said, things that don't have huge mass don't travel so aerodynamically and effectively through the air.
Impacts on Metal
Ballistic impacts on metal are usually distinguishable.
Neat margin on the entry side of the hole.
Exit side resembles a truncated funnel.
Friction between the bullet and metal generates heat.
The length and width of the funnel depend on the caliber and projectile velocity.
Recreating the impact in an experimental range can provide additional evidence.
The physical characteristics depend on the type of metal and bullet construction.
Different bullet designs (full metal jacket, armor-piercing) behave differently.
Impacts can result in dents, penetration, perforation, or ricochet.
Painted surfaces may exhibit specific cracking patterns.
Impacts on Wood and Frangible Materials
Frangible materials break up easily into smaller pieces (e.g. concrete).
Impacts on wood and frangible materials:
Neat entry hole.
Significant tearing and splintering on the exit side.
Debris is widely distributed.
Orientation of the material/target is important to determine the bullet's path.
Low velocity, large-caliber ammunition (handgun):
Causes significant splintering and larger exit holes.
High velocity, small-caliber ammunition (rifle):
Tends to create neater holes.
Softwoods splinter less than hardwoods.
Bone fractures from bullets are energy transfer related.
High velocity = Catastrophic effects.
Low velocity = Break or chip.
Impacts on Glass
Glass is a hard, frangible material with stored energy.
Firing into glass creates two features:
Concentric (circular) cracks around the bullet hole.
Radial cracks radiating laterally from the bullet hole.
Radial cracks will not cross other cracks.
The order of the shots can be determined by analyzing which cracks are stopped by others.
()Different types of glass are used depending on functions, therefore behavior can vary greatly.
Bulletproof glass is multi-layered.
Two panels of sheet glass, with a polycarbonate plastic layer.
Fabric Penetrations
Types of fiber
Behavior depends on whether the fiber is natural (cotton or wool) or synthetic (nylon, polyester).
Close range: Gunshot residue may be present.
White ring may be present.
Microscopy
Synthetic Fibers
Melted Individual fibers
Natural fibers
Torn fibers
Bullet hole wont be super clear.
Evidence from the Firearm User (Shooter)
Stressful situation can lead to more evidence being left on the shooter.
Inexperienced shooters:
May exhibit flash burns from holding the gun too high.
May grip the gun too tightly, leaving imprints.
Shotgun users may hold the gun incorrectly, leading to bruising.
Risk of being hit by fragments from the bullet impact.
Hearing damage from not wearing hearing protection.
Shooting Scene Investigation
Introduction
Shooting scene investigations encompass a broad spectrum of analyses critical for understanding what occurred during a shooting incident.
The primary goal is often a detailed shooting reconstruction to piece together the sequence of events.
Preparation for lab sessions includes understanding aerodynamic effects and air resistance, pivotal in trajectory analysis.
Reconstruction vs. Reenactment
Reconstruction
A science-based approach that hinges on physical evidence.
Relies on:
Physical evidence recovered from the scene.
Analyses of evidence using scientific methods.
Logical inferences derived from these analyses to build a coherent narrative.
Involves:
Meticulous collection of physical evidence, potentially spanning a wide area if the firearm or related items were moved post-incident.
Rigorous testing of various hypotheses to align with the evidence.
Aims to create an objective and accurate depiction of the shooting event, acknowledging potential limitations and variables.
Limitations:
Dynamic nature of scenes where people move and alter the environment.
Inherent limitations in precisely determining every detail to the millimeter.
Presents a spectrum of possible solutions grounded in the available evidence, offering insights into:
Potential locations of the shooter at the time of the incident.
Positions of all involved individuals during the shooting.
Movement of individuals and objects before and after the event.
Critical Considerations:
Overlapping evidence that may create complexities in interpretation.
Potential movement of evidence either intentionally or unintentionally.
Transfer of evidence, such as gunshot residue, from one location to another, including secondary transfer mechanisms.
Ballistics Expert Role:
Functions as a vital contributor within a multidisciplinary team, offering ballistics information.
Works in tandem with other forensic evidence such as fingerprints and DNA to construct a comprehensive understanding.
Operates independently of the police investigation to maintain objectivity.
Reenactment
A less scientific method compared to reconstruction.
Relies heavily on conjecture or subjective interpretations, which may lack scientific rigor.
May incorporate unreliable eyewitness accounts that can introduce bias.
Best used to test reconstructions, but the latter must be scientifically sound.
Objectives of Shooting Reconstruction
To aid the criminal justice system by providing clarity and insight into criminal events.
To answer fundamental questions, including:
Who was involved in the incident?
What exactly transpired during the shooting?
When did the events occur, establishing a timeline?
Where did the shooting take place, mapping the scene accurately?
How did the shooting unfold, considering all actions and factors?
Why did the shooting happen, examining motives and circumstances?
To understand key component factors involved in shooting incidents, such as:
Trajectories of bullets, accounting for external ballistics and environmental conditions.
Distances involved, distinguishing between close-range, contact, and long-range shootings.
Analysis of cartridge cases to link firearms to the scene.
Evaluation of bullet ricochet patterns to determine angles and directions.
Assessment of the effects of bullets passing through various materials to understand impact dynamics.
To either support or refute claims and testimonies presented in court, thereby ensuring a fair legal process.
To provide crucial assistance to legal and policing systems, facilitating the accurate identification and accountability of those responsible.
Initial Questions
Validate that a shooting occurred, ensuring definitive evidence.
Determine if a firearm was indeed used, as a bullet hole alone is insufficient evidence.
Essential evidence: Recovered bullet from a body, or embedded in a structure.
Consider alternative causes for holes to prevent misinterpretation.
Be aware that criminals often attempt to minimize or eliminate forensic evidence.
Avoid assumptions about a shooting based only on auditory evidence, such as hearing a loud bang without corroborating physical evidence.
Bullet Scenarios
Four Main Scenarios
Perforation: The bullet passes entirely through the target, creating both an entry and exit hole. This scenario indicates the bullet had sufficient energy to overcome the target's resistance.
Penetration: The bullet enters the target but does not exit. This occurs when the bullet's energy is fully absorbed by the target, preventing complete passage.
Fragmentation: The bullet breaks apart upon impact. Fragments may be retained within the target or pass through it, leading to a mixed pattern of penetration and perforation. This is common with certain types of ammunition designed to fragment easily.
Ricochet/Bounce: The bullet deflects off the surface upon impact, either remaining intact or breaking into fragments. This depends on the angle of impact and the material properties of both the bullet and the surface.
Different types of ammunition can behave differently upon impact, with some designed to break apart while others mushroom to increase the wound cavity.
Body armor works by dissipating energy over a large area, reducing penetration and protecting the wearer.
Analyzing Bullet Holes
Work backwards from where the bullet ends up to determine the trajectory and origin.
Trace the trajectory back from any exit wound to estimate the shooter's possible location.
Look for:
Bullets: Projectiles that may be lodged in structures or the victim.
Cartridges: Casings ejected from the firearm, which can link a specific weapon to the scene.
Fragments: Pieces of the bullet that broke apart upon impact.
Gunshot Residue (GSR): Deposits around the entry point, typically found only at close range and requiring confirmatory tests.
White Ring: A halo-like mark around entry holes, indicative of firearm use.
Hole Size and Shape: Characteristics that can indicate the type and caliber of the bullet.
High-Energy Penetration: Localized damage indicating the force of a bullet impact.
()Gunshot residue is only useful for close range, usually, up to a few meters or so. The particles are so small that they don't have huge mass and as we've already said, things that don't have huge mass don't travel so aerodynamically and effectively through the air.
Impacts on Metal
Ballistic impacts on metal typically leave distinctive marks.
Characteristics Include:
Neat Margin: Present on the entry side of the hole, indicating clean penetration.
Truncated Funnel Shape: Evident on the exit side, a result of metal deformation.
Heat Generation: Friction between the bullet and metal produces significant heat.
Caliber and Projectile Velocity: Dictate the funnel's length and width.
Experimental Recreation: Can offer additional comparative evidence by replicating the impact conditions in a controlled setting.
Physical Characteristics: Depend on the metal and bullet construction.
Bullet Design: Affects impact characteristics (e.g., full metal jacket vs. armor-piercing).
Types of Impacts: Ranging from dents and penetrations to perforations and ricochets.
Painted Surfaces: May reveal specific cracking patterns indicative of ballistic impact.
Impacts on Wood and Frangible Materials
Frangible: Materials that easily break into smaller pieces upon impact, such as concrete.
Impacts on Wood and Frangible Materials:
Neat entry hole
Significant tearing and splintering on the exit side
Debris is widely distributed
Trajectory Analysis: Requires understanding the target's orientation to determine the bullet’s path.
Low Velocity, Large-Caliber Ammunition (Handgun):
Causes significant splintering and larger exit holes.
High Velocity, Small-Caliber Ammunition (Rifle):
Tends to create neater holes.
Softwoods Splinter Less Than Hardwoods.
Bone Fractures from Bullets: Directly related to energy transfer.
High Velocity = Catastrophic effects
Low Velocity = Break or chip
Impacts on Glass
Glass: A hard, frangible material that stores energy and fractures in specific patterns when impacted.
Impacts Create:
Concentric (circular) cracks: Surrounding the bullet hole.
Radial Cracks: Radiating laterally from the point of impact.
Crack Propagation: Radial cracks will not cross other cracks, allowing the determination of the sequence of shots fired.
Order of Shots: Determined by assessing which cracks are interrupted by others.
()Different types of glass are used depending on functions, therefore behavior can vary greatly.
Bulletproof Glass: Constructed in multiple layers to enhance resistance.
Composition: Typically includes two panels of sheet glass with a polycarbonate plastic layer in between.
Fabric Penetrations
Types of fiber
Fiber Behavior: Varies between natural fibers (cotton, wool) and synthetic ones (nylon, polyester).
Close Range Indicators: Gunshot residue and white ring may be present.
Microscopic Analysis:
Synthetic Fibers: Melted Individual fibers
Natural fibers- Torn fibers
Bullet hole wont be super clear.
Evidence from the Firearm User (Shooter)
Stressful situations can lead to more evidence being left on the shooter due to heightened physical responses.
Inexperienced Shooters:
May exhibit flash burns from holding the gun too high.
May grip the gun too tightly, leaving imprints on the weapon.
Shotgun users can sustain bruising from incorrect handling.
Risk of being hit by fragments from the bullet impact.
Hearing damage from not wearing hearing protection