Introduction
A primary element in the analysis of many shooting incidents is distance determinationthe distance from the gun muzzle to the entry wound. The criteria most commonly used in this determination is the presence or absence of gunshot residue, the pattern diameter, and the type and distribution of gunshot residue. However, common protocols fail to consider the effect that hair may have upon the deposition of gunshot residue. There have been recent cases in which the absence of gunshot residue on the scalp was classified as evidence of a distant-range gunshot when other evidence supported a close-range gunshot.
In this manuscript, gunshot
residue is defined as visible soot deposit particles, not the usual
meaning of chemically or instrumentally detected primer and propellant
residues.
Hypothesis:
The presence of hair can significantly affect the deposition of
gunshot residue on skin.
Methodology
Hair
There is substantial variation in the characteristics of artificial hair used in wigs, and there are no available data supporting the relevance of artificial hair to human hair for the type of testing in this experiment. Although it was recognized that there is also considerable variation in human hair (i.e., length, curl, color, diameter, form) charactistics, human hair is a more valid model than artificial hair.
After investigating various sources and types of available human hair, life-sized mannequin heads with individually embedded human hair commonly used by cosmetologists were used. The mannequin heads are made in China and are available from most cosmetology schools.
Figures 1 - 3
The variation
in human scalp hair densities is great, from 0/cm for bald men to
approximately 400/cm2 (Olsen et al. 2001). Hair thickness,
type, and anatomic location as well as age, gender, and racial characteristics
also affect the density. A typical, full-headed human scalp will
have a density of approximately 300/cm2 (McElwe 2001).
Mannequin heads have an average density of approximately 325/cm2,
but they are different in follicular density because mannequins
have three to ten hairs in each scalp hole, whereas a human scalp
will have only one hair follicle per hole. This means that the density
of the hair directly above the scalp may be higher on a human head,
and the density of the mannequin scalp follicles (the hair shafts
protruding from the scalp) will be lower.
This difference is a positive element making the mannequin heads an effective comparison model because if gunshot residue can penetrate through the more dense mannequin hair, it will not likely be shielded by less dense, average, human head hair.
Protocol
One density factor was used so that gunshots at different distances could be compared meaningfully. Test shots were fired at a close range of 1 inch (2.5cm) and at an intermediate range of 4 inches (10cm). The weapon was shot into hair and nonhair areas. The differences in gunshot residue was compared and quantified.
To reduce variables, 24 shots were fired from one firearm and one type of ammunition.
- 24 Shots: 12 shots at 1 inch (2.5cm) and 12 shots at 4 inches (10cm)
- Weapon: Glock Model 19 (9mm)
- Ammunition: Winchester SXT Supreme 9mm, 147gr JHP with flattened ball powder
Results and Discussion
There was no grossly observable gunshot residue present in the areas covered by hair at the close (1 inch/2.5cm) or intermediate (4 inches/10cm) ranges. The hair served as an effective filter preventing the deposition of all forms of gunshot residue including burned and unburned powder particles, sooting, tattooing, and stippling.
Figures
4 and 5 are close-up images of mannequin
skin (left) and mannequin scalp (right). The hair has been partially
cut for examination purposes. Although there is a normal deposition
of gunshot residue on the bare skin, there is no visible residue
on the hair-shielded scalp.
Figures
4 - 5
Figures
6 and 7 are close-up images showing the
tests made from a close (1 inch/2.5cm) distance. The skin area has a dense gunshot residue deposit. When the same ammunition
and firearm are used at the same distance to fire into a hair-covered
scalp, there is no visible gunshot residue present. The hair was
partially cut for examination purposes.
Figure
6
Figure
7
Figures
8 and 9 show gunshots with and without
intervening hair that clearly display the difference in the presence
or absence of gunshot residue deposits. Also note the reduction
in the amount of bullet wipe; the hair not only filters out powder
particles, but it also absorbs a considerable amount of the carbonaceous
bullet-wipe material.
Figure
8
Figure
9
Case
Examples
Figure 10 shows a victim shot with a .410 shotgun
using disk-flake powder. Stippling and tattooing are visible in
the areas near the neck, but in the more hair-dense areas near the
top of the head there is an absence of similar gunshot residue stippling
or tattooing.
Figure
10
Figure
11 shows a wound caused by a flare gun that fired a homemade
12-gauge shotgun cartridge filled with screws, nuts, and other small
metal objects. Although it is not known if all the satellite defects
surrounding the central defect are the result of powder particles
or small metal projectiles, it is clear that the victim's hair,
which has been partially shaved, shielded the scalp from gunshot
residue and small projectile impact. Note the difference between
the upper, shaved scalp area and the forehead.
Figure
11
Test
1 Into Loose Bangs on Forehead
Figures
12 and 13 show the results of a gunshot
from 4 inches (10cm) through hanging hair. The gunshot residue stippling
or tattooing on the mannequin skin is clearly visible in the lower
areas near the cheek but fades into the upper areas near the top
of the head as the density of the hair increases. A close-range
shot higher into the forehead could result in a wound without any
visible gunshot residue. The ammunition used in this experiment
was Luke Haag reference ammunition 9mm FMJ with 8gr of "Accurate
No. 7" flattened ball powder (Haag 2000).
Figure
12
Figure
13
Test
2 Into Cotton Cloth
Many firearms
examiners perform pattern or distance testing by shooting into cotton
cloth that retains the gunshot residue and allows a visual display
of the pattern diameter at different distances. Figure 14
shows the result of a test using human hair that hung loosely against
the cotton test material while the pistol was fired from a 4-inch
distance. The hair did block a substantial proportion of the gunshot
residue, preventing most of it from reaching the cloth.
Figure
14
Observations
Movement
of Hair
During the preliminary experiments, it was noted that shots fired
from approximately 1 foot (30cm) or less would cause substantial
hair movement (Figure 15). This suggested that
the fast-moving gas preceding the bullet might push loose hair away
from the skin and allow gunshot residue to contact the underlying
skin.
Figure
15
Figure
16 shows that as a bullet leaves the muzzle, it is preceded
by a gas bubble that will at short distances make contact with a
victim's hair before the bullet.
Figure
16
Experiments
were performed using high-speed photography to analyze the dynamics
of the muzzle-gas effect on loose hair. The high-speed images (Figures
17 and 18) show the hair before and after
firing. Figure 18 shows the pistol has just fired; the slide has
started rearward. The bullet has entered and exited the mannequin's
head. The hair has not yet moved significantly but has been pushed
down against the head, not away from the bullet-strike point.
Figure
17
Figure
18
Loose,
Hanging Hair Dynamics
Experiments were also performed to test the movement of nonrooted,
loose, hanging hair. Figure 19 shows the movement
of loose, hanging hair as the bullet is fired through the hair into
the back of the neck. The sequence begins at the top left frame.
In the second frame, the gun has fired, and the bullet has exited
out the front neck area. Significant hair movement does not occur
until the fourth frame. (Frames show 1/60th second intervals.)
Figure
19
It was determined that the gas preceding the bullet does not move hair away from the bullet strike point. The muzzle gas may actually increase the hair density by flattening the hair against the skin or scalp.
Hair
Retains Gunshot Residue
Although hair can act as a shield or barrier against gunshot residue,
it also acts as an effective filter retaining much of the burned
and unburned powder particles. It is recommended that the hair overlying
an entry wound be carefully examined for gunshot residue. A comb
should be used to separate and collect residue particles. Figure
20 shows mannequin hair with gunshot residue particles.
Hair over a gunshot wound should always be retained as evidence,
even when gunshot residue has not been found. Burnett (1989) suggests
that the the particle form can be altered by impact.
Figure
20
Recommendations
Gunshot-range
determinations should always include consideration of the presence
of hair as an intervening, shielding object. This is particularly
true with gunshots into the face and other areas where long hair
strands could have been present when the shot was fired.
Bangs or loose hair strands, which may have been in place to shield a portion of a person's face, may no longer be in the same orientation and location when the victim is found. For example, a person with long hair covering part of the face may have been shot through the hair into the cheek or forehead while standing but be found in a prone position with the loose hair away from the face.
Without understanding the dynamics and the gunshot residue-shielding effects of hair, the absence of residue surrounding the face wound in an area possibly shielded by hair could be misinterpreted as a distant shot.
Distance determinations of gunshot-entry wounds under densely hair-covered areas should include an adhesive lifter, transfer, or direct application of colorimetric testing procedures, which may allow the visualization of the gunshot residue pattern (Glattstein et al. 2000A and 2000B). A method for lifting gunshot residue particles from hair and other objects is described in Zeichner and Levi (1993).
Hypothesis and Conclusions
The hypothesis is confirmed. The presence of hair can significantly affect the deposition of gunshot residue on skin.
- Hair can completely prevent the deposition of gunshot residue to the scalp and other hair-covered areas.
- An entry wound without stippling, sooting, or gunshot residue particles cannot be regarded as a distant-range shot without considering the presence of hair as an intervening object.
- Hair acts as an effective filter and will retain gunshot residue.
References
Burnett, B.
The form of gunshot residue is modified by target impact, Journal
of Forensic Sciences (1989) 34(4):808-822.
Glattstein, B., Zeichner, A., Vinokurov, A., and Shoshani, E. Improved
method for shooting distance determination. Part 2: Bullet holes
in objects that cannot be processed in the laboratory, Journal
of Forensic Sciences (2000A) 45(5):1000-1008.
Glattstein, B., Zeichner, A., Vinokurov, A., Levin, N., Kugel, C.,
and Hiss, J. Improved method for shooting distance estimation. Part
3: Bullet holes in cadavers, Journal of Forensic Sciences
(2000B) 45(6):1243-1249.
Haag, L. C. Reference ammunition for gunshot residue testing, Association
of Firearm and Tool Mark Examiners Journal (2000) 32(4):332-336.
McElwe, K. J. Department of Dermatology, Philipp Universitat, Marburg, Germany, personal communication, February 19, 2001.
Olsen, E. A., Cote, N., and Canfield, D. Age-Related Changes in Scalp Hair Density. Presented at the Third Intercontinental Meeting of the European Hair Research Society, Tokyo, Japan, 2001.
Zeichner, A. and Levi, N. Collection efficiency of gunshot residue
(GSR) particles from hair and hands using double-side adhesive tape,
Journal of Forensic Sciences (1993) 38(3):571-584.
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