Introducing Shooting Scene Investigations

Rifling in the gun barrel can tear small fragments from the bullet. Fragments adhere to bullet until it strikes a target.

Tape-lifting the bullet hole and the surrounding area can capture these microscopic fragments,

When analyzed might lead to the identity of bullet type and/or its country of origin.

NOT the same as volatilized GSR lead on the surface of the bullet. oStructurally, these are different:

GSR is characteristically spherical,Examined by Scanning Electron Microscopy and

X-Ray Fluorescence (SEM/EDX) and can have smooth contours. Torn fragments by the rifling of the barrel of the

weapon are rough and easily distinguished from GSR. The tape lift of this evidence should be protected like any tape-lifted trace evidence.

Trace Evidence: Rifling Fragments and GSR

Blood will be on bullet and on defect Theoretically if it hits two people, the blood from both - a

mixture of DNA - should be present. First person’s blood diluted after passing through the

second person, Detecting second person might be beyond the

capabilities of current technology. o Does not mean that it cannot be detected. If

detected, the first person’s blood … minor contributor to mixture., which can be important reconstruction information, although the actual results will be case specific.

o Not finding a second contributor does not necessarily mean the bullet failed to pass through a second person.

Blood from Bullets and Bullet Holes

Important for understanding what happened during the event.

Terminology confusing because bullet flight paths are sometimes erroneously referred to as trajectories

Flight path is determined in most shooting incidents, Not a trajectory

A true trajectory is a curved path, usually occurring over long distances that, is affected by gravity, diminishing velocity of the bullets and other factors.

Determining true trajectory of bullet requires an understanding the physics of trajectories and gravity, the velocity, caliber of the weapon, the ammunition used, muzzle velocity, wind characteristics, etc..

For most shooting incidents, true trajectory analysis is irrelevant because of the short distances involved – estimated to average 25 yards & are straight lines

Bullet Flight Paths

Trajectory for .308 Diameter 168 gr. JHP-BT @ 2800fps Muzzle VelocityTrue Trajectory

Basic Parameters & Components Long Range Trajectory

Bullet Flight Paths

Intermediate targets Requires investigation to determine what was hit. Recovered bullets help identify intermediate targets

Trace evidence present. Secondarily, packaging it properly to preserve trace evidence for

laboratory analysis.

Fatal Bullets Some fatal bullets found & identified during the autopsy. Bloody bullets @ scene not necessarily fatal projectile

Might have passed through someone’s arm or other soft tissue. Only the ME can determine which bullets were fatal.

On-scene bullet path angular component (coordinates) measurements.

If measurements erroneous, the bullet path determination will be incorrect

Positioning shooter positions incorrect.

Identifying Bullet Flight Paths

Defined as: Ending in fixed objects (walls, vehicles, furniture, etc) or are unfixed,

Passing through objects without a final terminus identified.

Bullet Paths Into Fixed Objects

Bullet Paths Into Fixed Objects

Bullet flight paths defined by angular components, vertical and azimuth. Bullet flight path’s angular components represent

how bullet’s journey is defined Essential part of the shooting incident

reconstruction. Required for reconstruction AND determining

shooter positions Footwear impressions, cartridge casings, etc

without angular components. Crucial for reconstructing shooting events.

Flight Path Angular Components

Use trajectory rods after determining that a bullet made the hole. Last step in the analysis of bullet holes Inserting something into hole can dislodge or ruin trace evidence present.

Perforating bullet strikes in fixed objects Two points of bullet contact: an entrance and an exit. Rod spans the gap between the entry and the exit.

Trajectory rods tell investigators where a bullet could not have come from . Improperly used rods

Bullet flight path inaccurate, Faulty determination of the location of shooter position(s) Flawed reconstruction.

Bad trajectory rod technique Sticking anything into a hole before trace evidence is collected and chemical

analysis is complete, Shoving something larger into the hole, such as a pen or pencil which ruins the hole

and leads to an erroneous bullet path determination, Not centering the rod in the hole using a carefully and gently placed centering

method, such as a rubber or cork with a center hole for the rod.

Determining Flight PathsUsing Trajectory Rods

Important Rod characteristics: Resistance to bending & weather, Linked together Attachable to lasers

Construction Metal rods that can be linked together in order to

attach to a laser. Problem >>> expensive … bend over time.

When out of round, useless for accurately determining bullet paths.

Wooden dowels Made into rods diameters closely mimic bullet

calibers. Can be sealed against moisture so that they do not warp.

Stiff plastic rods are also commercially available in multiple colors.

Drinking straws can be used if the circumstances are correct, but these are too short. They can, however, be used as a conduit for a laser beam.

Trajectory Rods

Laser with attached rod

Centering the rod

Angular Components of the Bullet Flight Path

Defined with respect to two important angular components … sometimes be @ scene: For vehicular shooting incidents, these are best determined

off-site .

The angular components are vertical and horizontal (azimuth): up-down and side-to-side. The vertical component is the North/South (up or down)

path, The azimuth is the horizontal East/West (left or right) path.

Describing each is critical because bullets travel in three dimensional planes - up or down and left-to-right or right-to-left. If path is neither an up or down nor left-to-right nor right-to-

left, they have no angular component.

Vertical Component

Defined: “The vertical component of a projectile’s reconstructed flight path. This angle is given a minus sign if the path followed by the projectile is downward and appositive sign if upward. A flight path that parallels a level surface has a vertical angle of 0.0o”.

Determining Vertical Component

Method 1. Photographic Use printout of photograph of the trajectory rod inserted into the bullet hole. Use trig functions to calculate determine the hypotenuse of a right triangle formed

with a plumb line, Print the photograph, follow the following steps:

Draw a right triangle on the printed photograph using the plumb line as the vertical reference.

Measure the three sides of the triangle using a ruler. Using these measurements, calculate the angle of impact using trigonometric

functions for a right triangle. Method 2: Use inclinometer placed on the trajectory rod,

Read vertical angular component from the dial. Photograph inclinometer reading.

Method 1

Method 2

Azimuth or Horizontal Angular Component

Defined:“An angle or bearing lying in the horizontal plan usually described on the basis of compass directions or with north, south, east, west descriptors. In shooting reconstruction, an arbitrary north-south or east-west reference line may be chosen as a reference or azimuth angles related to that line.”

Determined using a zero-edge protractor.

Place zero-edge protractor into place - the 90o line under the center of the bullet hole (under the trajectory rod)

Drop a plumb line against the outside edge of the trajectory rod so that it just touches the outer edge of the protractor and trajectory rod simultaneously.

Read the angle from where the vertical plumb line just touches the protractor If the line touches the protractor at the 75o mark,

compute the azimuth by subtracting from 90 (90-75 = 15o) and record the azimuth as 15o right-to-left (if bullet was travelling right-to-left.

Zero-edge Protractor

Determining AzimuthVehicle Shooting Scene

Determining Azimuth angle

– Trajectory rod through the hole

– Photographed from above intersection of probe & the string line

Horizontalreference

Bullet Paths Into Unfixed Objects

Determining accurate bullet flight paths nearly impossible.

Key word is accurate. Sometimes “ball park” estimates are possible. Situations occur when an unfixed intermediate target can move, such as curtains, clothing.

Approximating a bullet flight path Witness statements, Obvious signs of moved furniture, Footprints, Obstructions that confine the bullet path to a narrowed or loosely defined

area.

In these instances, and others, it might be possible to define a bullet’s possible area of origin and estimate an approximate path.

Bullet Flight Paths Through Unfixed Objects

Passenger’s Side Window Open

Driver’s SideWindow ½ Open

Maximum Positive and Negative Vertical Bullet Paths

Bullet Paths Through Vehicle

Inside Vehicle

View From Front of Vehicle Toward Rear

Positive and Negative Vertical Bullet Paths

Amount of Window Opening

Passenger’s Side Half Open

Driver’s SideWindow Half Open

Maximum Positive and Negative Vertical Bullet Paths

Passenger’s & Driver’s Half Open Windows

Inside Vehicle

View From Front of Vehicle Looking Rear

Positive and Negative Vertical Bullet Paths

Amount of Window Opening

Passenger’s Side Partially Open Driver’s Side

Window ClosedBullet Perforates Window

Maximum Positive and Negative Vertical Bullet Paths

Bullet Perforates Driver’s Window

Inside Vehicle

View From Front of Vehicle Toward Rear

Amount of Window Opening

Ricochet and Deflection

Travel in straight lines until they hit something. When that happens, several things might take place before the bullet finds its terminus.

The bullet can enter the object, It can go through the object, It can bounce or ricochet off the object

The point at which the bullet ricochets off an object is determined by several factors:

The structure and velocity of the bullet The physical characteristics of the surface The angle at which the bullet strikes the surface.

Generally, ricochet occurs at shallow angles of impact. As the impact angle becomes more acute, a point will be reached when

the bullet no longer ricochets and will enter the object. That angle is called the critical angle

Ricochet

Impact Surface

Ricochet

Perforation or fragmentation

Steeper Impact or Incident Angles

Ricochet Impact on BulletVelocity LossDeformation

Evidence transfer

Bullets Obey the Laws of PhysicsCritical Angle: Angle where ricochet no longer occurs

Term DefinitionAngle of Incidence “The angle at which a missile strikes a surface before ricocheting” (30)

“The intercept angle described by the pre-impact path of the projectile and the plane of the impact surface at the impact site when viewed in profile - differs from the NATO method. To convert, subtract 90 degrees minus the forensic angle defined above.”(31)

Angle of Impact “The angle of incidence of the impinging bullet or pellet to the substrate.” (30)

Angle of Ricochet “The angle at which a missile leaves a surface after ricocheting.” (30)“The angle formed between the path of the departing projectile subsequent to impact and the plane of the impacted surface.” (31)

Critical Angle “The actual degree at which a bullet will ricochet from a surface.” (30)“Angle at or below which a ricochet would be expected for a given bullet or pellet and a given substrate.” (29).“The incident (intercept) angle above which the particular projectile at a given impact velocity no longer ricochets from the impacted surface.” (31)

Ricochet “The deflection of a missile after impact.” (30) “A change in angle and/or direction of a fired bullet or pellet as a result of impact with a substrate.” (30)“The continued flight of a rebounded projectile and/or major projectile fragments after a low angle impact with a surface or object. “(31)

Ricochet Mark “A two-dimensional effect without discernible depth (such as a ricochet off an automobile windshield without surface penetration).” (30)

Ricochet Crease “A three-dimensional effect with discernible depth (such as a ricochet off an automobile hood).”

Deflection – as opposed to ricochet “A deviation in a projectile’s normal path through the atmosphere as a consequence of an impact with some object.” (31)

Deflection – as a consequence of ricochet

“Any lateral component of the ricocheted projectile’s departure path relative to the plane of the impacted surface as viewed from the shooter’s position and with the plane of the surface normalized to a horizontal attitude.” (31)

Deflection – as a consequence of perforating or striking an object

“Deviations in any direction from the projectile’s normal flight path as a consequence of perforating or striking an object rather than rebounding off surfaces.” (31)

Angle of Deflection “Lateral deflection (left or right) of a ricocheting bullet or pellet as it leaves a substrate.” (30)

Frangible surface “Surface that is subject to crumbling or breaking upon application of force, e.g., asphalt or concrete.” (30)

Non-frangible Surface “Surface that tends to bend or stretch upon application of force, e.g., sheet metal.” (30)

Language ofRicochet

Why does a bullet ricochet? The simple answer is that it hits a target at an angle less than the

critical angle for that surface and type of ammunition. A priori, it is impossible to know whether a bullet will ricochet. However,

there are characteristics of bullets that seem to foster ricochetNature of the bullet

The way the bullet is constructed such as hardness, weight, center of gravity and metallic components will impart, more or less, a tendency to ricochet.

Shape of the bullet Round nose bullets > flat ones. Full metal jacket rounds ricochet > lead alloy bullets.

Velocity Low velocity projectiles > high velocity.

Response of the surface A hard, unyielding surface versus a surface in which the bullet can

enter also affects how a bullet ricochets.

Tendencies to Ricochet

Soft or Yielding Surfaces Soft enough for the bullet to enter the surface’s

matrix, e.g., sheetrock, wood, automotive metal, etc.

For such surfaces, the impact/incident angle is generally smaller than the ricochet angle. Ricochet angle is typically greater than the

angle at which the bullet strikes the surface, o Not always true.

Surface Characteristics and Ricochet Angles

Soft or Unyielding Surface Ricochet Angle> Impact Angle

Bullet enters surface structure –shape of crease depends on

surface characteristics

Impact/Incident Angle

Surface

Bullet Ricochet AnglesSoft/Frangible and Hard Surfaces

Soft SurfacesWallboard

SodSand

Automotive Sheet Metal

Hard SurfaceRicochet Angle< Impact Angle

Bullet rides on surface

Hard/Frangible SurfacesGranite

Steel PlateStoneTile

AsphaltConcrete

Understanding characteristics of a particular surface can help locate bullet if not immediately obvious.

Theoretically, angle of impact can be approximated for some surfaces … dividing the width of the defect by length (w/l) and taking the arc sine of the fraction Same as calculating impact angle of bloodstains

Bullet impact angle and path can be inferred. Bullet/projectile striking a soft or yielding surface loses

velocity quickly and might not be as deformed as the same bullet/projectile striking a hard or unyielding surface.

Why are Surface Characteristics Important?

Yielding Surfaces: Bullet strikes the surface AND either enters or indents it. As the bullet travels

along the indentation forms, its shape “pushes” the surface material to form a “ramp” from which it can exit.

The ramp is steeper than the entry angle, which means the projectile exits at a larger angle than it struck.

Automotive sheet metal Bullets striking painted: specific diagnostic characteristics Direction of travel

Interaction with paint – pinch point Fracture lines on the edge of mark form on painted surfaces …. small stress

cracks that occur when bullet moves along surface and either ricochets or penetrate/perforates. o Point backward the direction from which the projectile was traveling, … o Visualize using dusting powder & lifting the powder with fingerprint lifting

tape … casting material (a better method), which also captures the physical characteristics of the ricochet/hole.

Lead-in mark at the entry point of the ricochet mark/hole.

Direction of TravelDetermined from Ricochet Mark

Refers to spin imparted to the bullet by the lands and grooves of the barrel of the gun, right or left as it heads to a target.

For hard, unyielding surface … rides along the surface longer tilted on its twisting side. If it has a right twist, spinning to right … leaves a mark visibly elongated on the right side.

The twist of the bullet causes it to rise up on its twisting side. When bullet exits, mark is longer on the side of the

twist, Certain marks have an elongation because the bullet

stays on the surface for a relatively long time. This elongated is known as a “Chisum Trail” after

criminalist Jerry Chisum.

Important … provides information about the bullet, even if never recovered. If, in a shooting incident, two bullets were recovered,

one with a right twist and the other a left, and both ricocheted off of a hard surface,

The twist information from the ricochet mark will tell investigators which struck which surface

TwistDetermination from Unyielding Surfaces

Rifling of a 105 mm Royal Ordinance L7 Tank Gun.

Additional surface characteristics must be considered. In addition to soft and hard surfaces

semi-hard and semi-yielding. Road asphalt.

On asphalt, forensic testing and other indicators can fail (indicators such as lead-in, pinch points).

A more reliable indicator of ricochet from asphalt results from the physical characteristics of the mark or crease is fresh, sharp, fragile edges.

oIf recognized early in the investigation before being worn away by traffic, investigators, or weather, they can be diagnostic of bullet impact. Uneven nature of asphalt, ricochet and deflection angles are unpredictable.

oBullet might have a right twist, but the deflection might be to the left simply because the bullet struck a small stone that was part of the physical integrity of the asphalt.

Surfaces with Frangible (Crushable) Materials

Surfaces that tend to crumble when struck by a bullet/projectile: Cinder block, bricks and stones cast from mortar. React like hard or unyielding surfaces until the combination of the impact velocity and

the incident/impact angle causes the material to shatter below the impact site, Makes ricochet angle sometimes less than the incident angle –

oSimilar to a hard surface.

Semi-hard or Semi-yielding Surfaces

Impact surfaces are categorized as yielding, unyielding, semi-hard or semi-yielding or frangible. Each has characteristics that affect ricochet.

Bullet/projectile loses velocity, more so in yielding surfaces

Bullet/projectile departs surface at an angle other than its incident angle, which varies depending on the specific surface.

Bullet/projectile may deform or fragment, the amount of which depends on the surface characteristics. Yielding surfaces may not deform the bullet at all.

The struck surface may deform or breakup, such as with frangible materials, the resulting ricochet

Mutual evidence transfers take place between bullet/projectile and impact surface

Summary of Ricochet Effects

Occurs when a bullet/projectile deviates from the plane of its incident/impact angle. Ricochet How bullet/projectile interacts with the surface.

Semi-hard surfaces such as asphalt. o The bullet/projectile strikes the asphalt and interacts with the

surface. If the bullet strikes something hard in the asphalt, such as a stone, it can deflect unpredictably.

Bullet/projectile can perforate surface & exit in a different plane. That is, deflection occurs to the right, left, up or down … Direction of the deflection equals twist of the bullet. Bullet enters

the material, spinning. Given the correct conditions, if the bullet has a right twist, it will deflect to the right.

Bullet must be in contact with the interior of the material for a period of time, depending on the material, to allow it to ‘grab’ the texture of the surface sufficiently for it to change direction.

Thin materials - sheet metal - little or no deflection.

Deflections

FirearmsFirearms should be treated as though they might have

blood and fingerprints present because these are individualizing types of evidence that might identify the shooter and/or the victim.

Logistics of preserving that evidence and other ballistics evidence must take into consideration the necessary steps to render the firearm safe. Always ignore the impulse to handle and examine weapon

as closely as possible. Most shooting scene investigators understand it is bad

practice to stick anything into the barrel to examine the weapon.

Packaging/Preserving Firearms Evidence

Specific sequential steps in handling the weapon. Archive the position of the weapon at the scene through sketches and photography Carefully pick up the weapon using a gloved hand by holding it at the extreme end of the

barrel and the area of the handle not usually touched when firing the weapon. Render the render the weapon safe by ensuring the safety is on.

Inspect the chamber for live rounds and remove any present and package carefully as described below for bullets.

For semi-automatics, remove the magazine, leaving the rounds inside. Package it separately for subsequent fingerprint analysis by securing it between cardboard in an evidence box, ensure that it will not shift during transit.

For revolvers, photograph or record the relative position each round in the cylinder. Record weapon specific information: serial number, make, model and caliber of the weapon. Mark the all weapons with an identifying evidence number, the initials of the collecting officer

and the date. Ensure that it is marked in an area that will not destroy evidence. Place all firearms in evidence boxes designed to carry firearms, ensuring that the weapon

cannot shift during transit. Do not clean the bore or chamber before packaging the weapon. Do not ship firearms with bullets in the chamber.

Packaging/Preserving Firearms Evidence

Firearms

Bullets

The focus on shooting incidents is usually on bullets. Certainly this is understandable because they can carry important forensic information.

For this reason finding, collecting and preserving bullets is a critical part of the scene investigation. Collect all bullets because each individual bullet at the scene might not have sufficient rifling characteristics to make a specific identification of the firearm employed.

Recover ALL bullets and archive their position through sketches and photography. Each bullet should have a unique evidence identification number.

Never touch a bullet with an ungloved hand. Never touch the ogive (point) area of a bullet because it might remove important fragile

trace evidence, such as hairs, or fibers, etc. Handle bullets with non-metallic tweezers because metallic tweezers can put scratches on

the bullet that can interfere with the interpretation of their meaning and importance with respect to reconstruction of the incident.

Never mark bullets to identify them for the same reason as above. Wrap bullets in soft paper or tissue and seal in separate pill boxes or envelopes. Pack the

pill box with paper to ensure that the bullet will not move during transit. Label and seal the container appropriately.

Packaging/Preserving Firearms Evidence

Cartridge Cases

Carry important forensic information (markings from the breech clock, firing pin, ejector, etc. ) Ensure not marked further during the investigative process. Archive cartridge case evidence through sketches and photography. Each should have its own

evidence identification number. Handle cartridge cases with gloved hands Pick up at the ends of the case (Not the breech end).

This will ensure that any fingerprint evidence on the barrel of the case is as preserved as much as possible.

Do not mark brass cartridge cases. Fired shotgun shells can be on inside or outside of the paper or plastic.

Package each cartridge case in a separate container prepared as described above for bullets.

Ammunition

All unused ammunition not inside weapons should be recovered … vehicles, suspects, clothing, houses, etc. Treat as bullets. If unused ammunition is in boxes, the outside of the box should be marked appropriately.

Powder and Shot Patterns

Powder patterns found on skin of victims (fouling and/or stippling) or clothing. Preserve patterns photographically and if possible collect the evidence, e.g., clothes, at the scene

and package sufficiently well so that there is no transfer of evidence from one part to another. Appropriate way to package GSR on clothing is to wrap clothing in paper as though preserving

bloodstain evidence.

Packaging/Preserving Firearms Evidence

Cartridge Case Ejection Patterns

Cartridge Case Ejection PatternsFactors affecting

• Factors that affect ejection patterns– Type of ammunition– Shooter’s hand-hold– Body position– Shooter’s movement (walking/standing)– Ground surface– Environmental factors

• Caution in reaching conclusions– Nothing is absolute

• Movement @ scene by investigators• Movement @ scene by vehicles

Determining Cartridge Case Ejection Patterns

Cartridge Case Ejection PatternEffect of Vertical Angle Changes

.40 Caliber Glock: Winchester 180 gr. JHP Ammunition

Cartridge Case Ejection Pattern

Sketching Shooting Scenes

Deck

Shell Casing

Bullet Path

Angle of Impact

Ricochet Angle

Sketching Shooting Scenes

Deck

Door

BIM

Trace Evidence on Bullet

Rear of Car

Inside Trunk of Car

Shoot-em up car

Bullet Hole In Rear Window

Bullet RicochetOn Speaker

Bullet Hole in Rear Tail Light

Hole in Window

Bullet Hole in Rear SeatHeadrest

Bullet Hole in Rear SeatSpeaker

Trajectory Rods inBack seat

Trajectory Rods inTrunk

Trajectory Rod ThroughRear Tail Light

Trajectory of Bullet Through the Car