Shooting Scene Investigation: Evidence on Shooters, Scene Documentation, and Trajectory Analysis lect 9

Evidence on Shooters

• Inexperienced shooters often hold weapons incorrectly and tightly, increasing the likelihood of acquiring evidence on themselves.

• Shooting is stressful, leading to the acquisition of evidence.

Slide Bite

• Occurs when holding a self-loading pistol too high on the grip. The slide rubs against the hand during cycling.

• The slide, moving backward to cycle the firearm, may cause scratches and abrasions, potentially leading to bleeding between the forefinger and thumb.

• These injuries are unusual because cuts between the forefinger and thumb are not typical.

• Slide bite indicates potential gun involvement, though not definitive.

Hammer Bite

• Similar to slide bite; occurs with self-loading pistols that have external hammers.

• As the slide pushes the hammer back, it can imprint or abrade the skin between the forefinger and thumb if the weapon is held too high.

• Hammers are often textured for better grip, enhancing abrasion and DNA collection.

• Textured surfaces on firearms, such as pistol and hammer grips, are excellent sources of DNA due to frequent skin contact.

Shotgun Recoil and Bruising

• Inexperienced users may hold shotguns incorrectly, leading to significant bruising on the forearm.

• Shotguns have high energy, and incorrect handling can cause trauma.

• Bruising on the forearm suggests firearms use, particularly if the shotgun is not held properly against the shoulder.

• Holding the shotgun against the shoulder distributes recoil across a larger mass.

Grip Imprints

• Tight grips on firearms with textured surfaces can leave temporary imprints on the hands due to recoil, especially when grasping the weapon tightly

Scope Bite

• Inexperienced rifle shooters may place their eye too close to the optical scope. Recoil can cause the scope to hit the area between the eyes, resulting in a "scope bite."

• Experienced shooters maintain an offset to avoid injury.

• Using proper techniques can prevent injuries.

Scene Documentation

• Document the scene. Scene mapping includes scaled plans, sketches (ideally to scale), and contemporaneous notes.

• Document the scene in three dimensions to account for bullet trajectory.

• Bullet trajectory is a three-dimensional entity

• Consider the left-right direction relative to fixed data points and the elevation (up-down).

Two-Dimensional Views

• Create side-on and top-down views of the scene.

• Side-on views illustrate the up-down of the bullet trajectory

• Top-down views illustrate the left-right bullet trajectory

Digital Models

• Digital models can visualize the scene, aiding in court presentations.

Determining Shooter Location

Eyewitness Accounts

• Use eyewitness accounts cautiously due to potential inaccuracies from fight or flight instincts.

• Witness recall may be unreliable because heightened states of emotion shuts down part of the brain which affects recall.

• Consistent accounts from multiple witnesses can provide a starting point, but scientific proof is necessary.

Bullet Trajectories

• Determine trajectory and bullet velocities.

• In internal scenes, assume a straight bullet trajectory because the distance traveled over a small room is not that far.

• In external scenes, account for bullet drop due to gravity over long distances.

Gunshot Residue (GSR)

• Test the area for gunshot residue (GSR) to confirm the shooting.

• GSR from the barrel and chamber goes in multiple locations.

• In long-range shootings, look for GSR at the shooter's location, not the target.

• GSR may contain a mixture of residues from different types of ammunition.

Cartridge Ejection Patterns

• Analyze cartridge ejection patterns, noting the direction and distance cartridges travel.

• The direction and distance depend on the weapon and ammunition.

• Experimental firing of a suspect weapon can determine typical ejection patterns.

• The ejection patterns will help pinpoint where the shooter was.

• Cartridge location also depends on how the shooter held the firearm (e.g., from the hip versus held high).

Trajectory Analysis

• Start analysis at the bullet hole and work backward to determine the shooter's location.

Tools for Trajectory Analysis

• Stringing kits: Physical strings across the scene.

• Angle gauges: Measure the angle of trajectory relative to the horizontal.

• Bubble levels: Ensure flat lines for measurements.

• Trajectory rods: Attach lasers to show trajectory.

• Protractors: Measure angles.

Strings

• Strings are inexpensive and easy to understand for juries.

• Problems include lack of rigidity

• They need tension to fix them.

Lasers

• Laser trajectories overcome string issues.

• They are useful for non-penetrating impacts.

• Class three lasers have the potential to do damage and should be used with care. Lasers have a high visibility to viewers.

Centering Cones

• Centering cones help determine the bullet's path.

• The cone is placed within the hole to follow the path of least resistance to determine the entrance point.

Trajectory Examples

• Examples shown for bullet holes in car doors.

• Centering cones guide trajectory rods.

• Lasers attached to rods show the bullet's path.

• Angle gauges measure trajectory angles.

• Zero base protractors are used.

• Plumb lines establish vertical lines of reference.

Bullet Hole Analysis

• The shape of the bullet hole can help approximate the angle of impact.

• If the bullet hole is a perfect circle, it hit at 90 degrees.

• An oval shape indicates an angle.

Angle of Impact Calculation

• Angle = sin^{-1}(Width / Length)

• The angle of impact is equal to the inverse sine of width over length.

• Same calculation that's used in blood spatter analysis.

Trajectory in Vertical and Horizontal Planes

• Measure angles to predict angles, vertically and horizontally.

Vertical Plane (Side View)

• Side view illustrates up-down trajectory.

• The bullets went, and how high it was relative to a fixed point

Horizontal Plane (Top View)

• Top view illustrates left-right trajectory.

• Bird's eye view as the bullets impact on the wall from a right to left or left to right.

Ricochet and Deflection

• Ricochet is the general sense of a bullet to change direction.

Ricochet

• Is a specific bounce off of a surface

• Involves the up-down plane (side view).

• Angle of incidence: The angle at which the bullet impacts the surface.

• Angle of ricochet: The angle at which the bullet comes off the surface.

• angle{incidence} \neq angle{ricochet}

Deflection

• Involves lateral movement (left-right plane, top view).

• Deflection often follows the twist of the bullet.

• Angle of deflection: Angle on left or right plane.

Evidence on Shooters

• Inexperienced shooters tend to exhibit several behaviors that increase the likelihood of acquiring evidence on themselves:

  • Incorrect Weapon Handling: Often hold weapons incorrectly and tightly, leading to a higher chance of leaving fingerprints, DNA, or experiencing firearm-related injuries.

  • Stress-Induced Actions: Shooting is a high-stress activity, potentially causing the shooter to sweat, breathe heavily, or make other movements that transfer biological material onto the firearm or surrounding environment.

Slide Bite

• Definition: A "slide bite" occurs when an individual holds a self-loading pistol too high on the grip, allowing the slide to rub against the hand during the cycling process.

  • Mechanism: As the slide moves backward to cycle the firearm, it can cause friction against the skin, resulting in scratches, abrasions, and potential bleeding between the forefinger and thumb.

  • Indicators:

  • Location: Cuts or abrasions between the forefinger and thumb are not typical injuries, making them indicative of potential firearm involvement.

  • Significance: While not definitive proof, a slide bite suggests the individual may have been handling a firearm improperly.

Hammer Bite

• Definition: Similar to a slide bite, a "hammer bite" occurs with self-loading pistols that have external hammers.

  • Mechanism: When the slide pushes the hammer back, it can imprint or abrade the skin between the forefinger and thumb if the weapon is held too high.

  • Texture:

  • Hammers are often textured to provide a better grip, which enhances abrasion and facilitates DNA collection.

  • Textured surfaces on firearms, such as pistol and hammer grips, are excellent sources of DNA due to frequent skin contact.

Shotgun Recoil and Bruising

• Incorrect Handling: Inexperienced users may hold shotguns incorrectly, leading to significant bruising on the forearm.

  • High Energy: Shotguns have high energy, and incorrect handling can cause trauma.

  • Distribution of Recoil: Holding the shotgun against the shoulder distributes recoil across a larger mass, reducing the risk of bruising.

  • Indicators: Bruising on the forearm suggests firearms use, particularly if the shotgun is not held properly against the shoulder.

Grip Imprints

• Temporary Marks: Tight grips on firearms with textured surfaces can leave temporary imprints on the hands due to recoil, especially when grasping the weapon tightly.

Scope Bite

• Definition: Inexperienced rifle shooters may place their eye too close to the optical scope. Recoil can cause the scope to hit the area between the eyes, resulting in a "scope bite."

  • Experienced shooters:

  • Maintain an offset to avoid injury.

  • Injuries can be prevented by using proper techniques.

Scene Documentation

• Importance: Documenting the scene thoroughly is crucial for accurate analysis and reconstruction.

  • Scene mapping includes:

  • Scaled plans

  • Sketches (ideally to scale)

  • Contemporaneous notes

  • Three-Dimensional Documentation: Document the scene in three dimensions to account for bullet trajectory.

Bullet Trajectory

• Three-Dimensional Entity: Bullet trajectory is a three-dimensional entity, requiring consideration of multiple axes.

  • Assessment:

  • Left-Right Direction: Relative to fixed data points.

  • Elevation (Up-Down): Vertical angle of the trajectory.

Two-Dimensional Views

• Creation

  • Side-On Views: Illustrate the up-down of the bullet trajectory.

  • Top-Down Views: Illustrate the left-right bullet trajectory.

Digital Models

• Usage: Digital models can visualize the scene, aiding in court presentations and jury understanding.

Determining Shooter Location

Eyewitness Accounts

• Reliability: Use eyewitness accounts cautiously due to potential inaccuracies from fight or flight instincts.

  • Witness Recall: May be unreliable because heightened states of emotion shuts down part of the brain, affecting recall.

  • Verification: Consistent accounts from multiple witnesses can provide a starting point, but scientific proof is necessary.

Bullet Trajectories

• Essential data:

  • Determine trajectory and bullet velocities.

  • Internal Scenes: Assume a straight bullet trajectory because the distance traveled over a small room is not that far.

  • External Scenes: Account for bullet drop due to gravity over long distances.

Gunshot Residue (GSR)

• Analysis: Test the area for gunshot residue (GSR) to confirm the shooting.

  • GSR Dispersion: From the barrel and chamber goes in multiple locations.

  • Long-Range Shootings: Look for GSR at the shooter's location, not the target.

  • Composition:GSR may contain a mixture of residues from different types of ammunition.

Cartridge Ejection Patterns

• Examination: Analyze cartridge ejection patterns, noting the direction and distance cartridges travel.

  • Dependency: The direction and distance depend on the weapon and ammunition.

  • Experimental Firing: Of a suspect weapon can determine typical ejection patterns.

  • Shooter Location: The ejection patterns will help pinpoint where the shooter was.

  • Affecting Factors: Cartridge location also depends on how the shooter held the firearm (e.g., from the hip versus held high).

Trajectory Analysis

• Method: Start analysis at the bullet hole and work backward to determine the shooter's location.

Tools for Trajectory Analysis

• Common tools include:

  • Stringing kits: Physical strings across the scene.

  • Angle gauges: Measure the angle of trajectory relative to the horizontal.

  • Bubble levels: Ensure flat lines for measurements.

  • Trajectory rods: Attach lasers to show trajectory.

  • Protractors: Measure angles.

Strings

• Characteristics:

  • Inexpensive and easy to understand for juries.

  • Problems include lack of rigidity

  • They need tension to fix them.

Lasers

• Benefits: Laser trajectories overcome string issues.

  • Application: Useful for non-penetrating impacts.

  • Safety: Class three lasers have the potential to do damage and should be used with care. Lasers have a high visibility to viewers.

Centering Cones

• Function: Centering cones help determine the bullet's path.

  • Usage: The cone is placed within the hole to follow the path of least resistance to determine the entrance point.

Trajectory Examples

• Application:

  • Examples shown for bullet holes in car doors.

  • Centering cones guide trajectory rods.

  • Lasers attached to rods show the bullet's path.

  • Angle gauges measure trajectory angles.

  • Zero base protractors are used.

  • Plumb lines establish vertical lines of reference.

Bullet Hole Analysis

• Assessment:

  • The shape of the bullet hole can help approximate the angle of impact.

  • Perfect Circle: If the bullet hole is a perfect circle, it hit at 90 degrees.

  • Oval Shape: Indicates an angle.

Angle of Impact Calculation

• Formula: Angle = sin^{-1}(Width / Length)

  • Definition: The angle of impact is equal to the inverse sine of width over length.

  • Relevance: Same calculation that's used in blood spatter analysis.

Trajectory in Vertical and Horizontal Planes

• Angular Measurements: Measure angles to predict angles, vertically and horizontally.

Vertical Plane (Side View)

• Illustration: Side view illustrates up-down trajectory.

  • Bullet Path: The bullets went, and how high it was relative to a fixed point

Horizontal Plane (Top View)

• Illustration: Top view illustrates left-right trajectory.

  • Perspective: Bird's eye view as the bullets impact on the wall from a right to left or left to right.

Ricochet and Deflection

• Ricochet is the general sense of a bullet to change direction.

Ricochet

• Specifics:

  • Is a specific bounce off of a surface

  • Involves the up-down plane (side view).

  • Angle of incidence: The angle at which the bullet impacts the surface.

  • Angle of ricochet: The angle at which the bullet comes off the surface.

  • Angle difference: angle{incidence} \neq angle{ricochet}

Deflection

• Characteristics:

  • Involves lateral movement (left-right plane, top view).

  • Deflection often follows the twist of the bullet.

  • Angle of deflection: Angle on left or right plane.