Introducing Shooting Scene
Investigations
Trace Evidence:
Rifling Fragments and GSR
 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.
o Structurally, these are different:
 GSR is characteristically spherical,
 Examined by Scanning Electron Microscopy and XRay 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.
Blood from Bullets and Bullet Holes
 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.
Bullet Flight Paths
 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
Trajectory for .308 Diameter 168 gr. JHP-BT
True Velocity
Trajectory
@ 2800fps Muzzle
Basic Parameters & Components
Long Range Trajectory
Bullet Flight Paths
Identifying 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.
Bullet Paths Into Fixed Objects
 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
Flight Path Angular Components
 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.
Determining Flight Paths
Using Trajectory Rods
 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.
Trajectory Rods
 Important Rod characteristics:
 Resistance to bending & weather,
 Linked together
 Attachable to lasers
Centering the rod
 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
Laser with attached rod
are correct, but these are too short. They can,
however, be used as a conduit for a laser beam.
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-toleft, 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 (9075 = 15o) and record the azimuth as 15o right-toleft (if bullet was travelling right-to-left.
Zero-edge Protractor
Determining Azimuth
Vehicle Shooting Scene
Determining Azimuth
angle
– Trajectory rod through the
hole
– Photographed from above
intersection of probe & the
string line
Horizontal
reference
Bullet Paths Into Unfixed Objects
Bullet Flight Paths
Through 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 Paths Through Vehicle
View From Front of Vehicle Toward Rear
Passenger’s Side
Window Open
Inside Vehicle
Driver’s Side
Window ½ Open
Maximum Positive and Negative
Vertical Bullet Paths
Positive and Negative
Vertical Bullet Paths
Amount of Window Opening
Passenger’s & Driver’s Half Open Windows
View From Front of Vehicle Looking Rear
Driver’s Side
Window Half Open
Passenger’s Side
Half Open
Inside Vehicle
Maximum Positive and Negative
Vertical Bullet Paths
Positive and Negative
Vertical Bullet Paths
Amount of Window Opening
Bullet Perforates Driver’s Window
View From Front of Vehicle Toward Rear
Passenger’s Side
Partially Open
Inside Vehicle
Driver’s Side
Window Closed
Bullet Perforates Window
Maximum Positive and Negative
Vertical Bullet Paths
Amount of Window Opening
Ricochet and Deflection
Ricochet
 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
Bullets Obey the Laws of Physics
Critical Angle: Angle where ricochet no longer occurs
Steeper Impact
or Incident Angles
Ricochet
Impact Surface
Ricochet Impact on Bullet
Velocity Loss
Deformation
Evidence transfer
Perforation
or fragmentation
Term
Definition
Angle 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)
“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)
Critical Angle
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).”
“A deviation in a projectile’s normal path through the atmosphere as a consequence of
an impact with some object.” (31)
“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 opposed to ricochet
Deflection – as a consequence of
ricochet
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)
“Surface that is subject to crumbling or breaking upon application of force, e.g., asphalt
or concrete.” (30)
“Surface that tends to bend or stretch upon application of force, e.g., sheet metal.” (30)
Frangible surface
Non-frangible Surface
Language of
Ricochet
Tendencies to Ricochet
 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 ricochet
Nature 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.
Surface Characteristics
and Ricochet Angles
 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.
Bullet Ricochet Angles
Soft/Frangible and Hard Surfaces
Soft or Unyielding Surface
Ricochet Angle> Impact Angle
Bullet enters surface structure –
shape of crease depends on
surface characteristics
Hard Surface
Ricochet Angle< Impact Angle
Impact/Incident Angle
Surface
Soft Surfaces
Wallboard
Sod
Sand
Automotive Sheet Metal
Bullet rides on surface
Hard/Frangible Surfaces
Granite
Steel Plate
Stone
Tile
Asphalt
Concrete
Why are Surface
Characteristics Important?
 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.
Direction of Travel
Determined from Ricochet Mark
 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.
Twist
Determination from Unyielding Surfaces
 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
Rifling of a 105 mm Royal
Ordinance L7 Tank Gun.
Semi-hard or Semi-yielding Surfaces


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 leadin, 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.
o
If 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.
o
Bullet 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 –
o
Similar to a hard surface.
Summary of Ricochet Effects
 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
Deflections
 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.
Packaging/Preserving
Firearms Evidence
Firearms
Firearms 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
Firearms
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
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.
Cartridge Case Ejection Patterns
Cartridge Case Ejection Patterns
Factors 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 Pattern
Effect of Vertical Angle Changes
.40 Caliber Glock: Winchester 180 gr. JHP Ammunition
Cartridge Case Ejection Pattern
Sketching Shooting Scenes
Sketching Shooting Scenes
Trace Evidence on Bullet
Deck
Deck
BIM
Shell Casing
Door
Angle of Impact
Ricochet
Angle
Shoot-em up car
Rear of Car
Inside Trunk of Car
Bullet Hole In Rear Window
Hole in Window
Bullet Ricochet
On Speaker
Bullet Hole in Rear Tail Light
Bullet Hole in Rear Seat
Headrest
Bullet Hole in Rear Seat
Speaker
Trajectory Rods in
Back seat
Trajectory Rods in
Trunk
Trajectory Rod Through
Rear Tail Light
Trajectory of Bullet Through the Car