Examination of Physical Evidence
Introduction
What is physical evidence? Physical evidence can be defined as ‘any object, mark or
impression that originates from a non-living object’ (Annets, 2010). Given the loose
definition there is a broad spectrum of evidence that falls into this category, all of which can
provide crucial information of the crime being investigated. The main areas of physical
evidence looked at in this report are the analysis of ballistics, footwear marks, tool marks,
documents, IT and fibres.
1) Ballistics
Ballistics can be defined as the science of firearms. Firearms are classed as ‘any lethal
weapon that uses a burning propellent to discharge one or many projectiles’ (Annets, 2010).
According to Fitchett, 2010, ballistics itself can be categorised into three groups, internal,
external and terminal ballistics. These groups refer to the different stages a firearm goes
through from the internal workings before and just after the bullet has been fired (the
internal ballistics), to the bullet leaving the gun until it reaches the target (external
ballistics), to finally what happens when the bullet makes impact with the target (terminal
ballistics). Each stage can provide crucial information to investigators, whose objective is to
identify the model of the firearm used and eventually the person (if not already caught) who
used the firearm.
The Projectile
Firearms have bullets that are found within cartridge cases that contain the primer and
powder required to create an excess build-up of gas in order to fire the bullet at high
speeds. The cartridges and bullets both eject from the barrel and if left at
the scene can provide immensely useful information about the model of
the firearm. A visual inspection of the cartridge’s base, usually aided by a
microscope, will reveal the head-stamp. Head-stamps are a form of
identification marker produced by the manufacture, it will usually include
the calibre size (which is the internal diameter of the firearms barrel) and Figure 1.1
(PSACFO, 2015) –
identify the manufacture. An example of a headstamp can be seen in Headstamp
figure 1.1. example
A visual inspection of the bullets can show multiple identification markers
produced on the bullets while in the barrel of the gun/when they are fired.
One of the identifying marks present may be rifling marks; as seen in figure
1.2. Rifling is created due to spiralling lands and grooves within the barrel
of the firearm used to give the bullet stability when shot. The lands and
grooves are engraved on the bullet when propelled out of the firearm at
high speed; the number of lands and grooves and the twist rate can aide
Figure 1.2 (Scientific
identifying the manufacturer/model.
American, 2005) –
Example of rifling
marks
, Furthermore, any irregularities or unique markings on the bullets are referred to as the
“ballistic fingerprint” (Annets, 2010). These are extremely useful if a firearm has been
recovered as the firearm can be used to “test-fire” (NIST, 2016). By using the same gun and
another bullet a comparison between the bullet found at the scene and the test. This
comparison may reveal the same ballistic fingerprint marks and link the bullet to the
firearm.
Lastly, microstamping is another form of identification mark
on the bullet casing. Microstamping is caused by an etching
on the firing pin created during manufacturing that leaves an
impression on the bullet casing when the pin strikes the
casing. The etching includes information about the make and
model of the firearm and a unique serial number. If recovered
from the scene a microscope can be used to identify these
marks and search a data base for further information. Figure 1.3 (Symon, 2020) – Example of
microstamping
Damage Caused
The make and model of firearms can create unique patterns upon impact with a target that,
when analysed, can indicate important information about the gun but also the placement of
the shooter. The damage caused by firearms are most commonly found on victims rather
than property and a visual analysis of calibre wounds can “establish the circumstances when
the firearm was fired” (Annets, 2010). In calibre wounds the bullet either fully penetrates
the body and crates an entry and exit wound or it becomes lodged in the body so only an
entry wound is present. The features of the wound are dependent on the energy of the
projectile which is affected by the distance away from the target. The blood stain patterns
can help determine the way the victim was facing when shot, back splatter (created form
the entry wound) is found in smaller drops almost like a mist whereas forward splatter
(created form the exit wound) is denser in distribution and found in a larger surrounding
area. Lastly, the trajectory of the firearm is usually determined by a specialist by measuring
angles, using lasers and trigonometric equations to calculate where the bullet came from
and even the heigh of the shooter.
2) Footwear Marks
Footwear marks are impressions created when the sole of a shoe creates a unique mark that
is either two-dimensional or three-dimensional. Two-dimensional footwear marks refer to
the deposit of materials accumulated on the sole of a shoe through being worn, providing
either a latent or an observable footwear mark. Whereas three-dimensional footwear marks
refer to marks that have created an impression on a surface that has given the footwear
mark depth. Both forms of footwear marks should be photographed with scales included
before they are disturbed. After being photographed their analysis differs to gain the most
observable prints for visual inspection.
Three-dimensional Footwear Marks
Dent Stone Casting
