Transcript Identifying Sharp-Force Trauma-Serrated vs. Non

Identifying Sharp-Force Trauma-Serrated vs. NonSerrated Blades
Martha Kools, Taylor Maddox and Carlos Sanchez
Abstract
The purpose of this study is to determine the accuracy of techniques
devised to identify characteristics of knives used to inflict damage on
bone. According to the FBI’s Unified Crime Report, of the nearly
12,000 people murdered in 2014, over 1,500 were killed by sharp
force trauma with cutting instruments. While much research has
been dedicated towards understanding the different effects on bone
caused by sharp and blunt force trauma, forensic anthropology is
only beginning to differentiate between individual weapons.
Currently, perimortem trauma associated with knives is understood
to present as predominantly clean, linear puncture damage, rarely
exhibiting radiating or concentric fractures; however, it has been
observed that different types of knives create distinctive features.
Thompson and Inglis (2009) found that fracture patterns from stab
marks could indicate the use of either a serrated or non-serrated
blade. To test this hypothesis, this study will measure stab wounds
inflicted by a third party on the ribs of a domestic pig, and identify
them as either serrated or non-serrated. An error rate will then be
calculated to determine the overall precision of the technique.
Introduction
Methods
For this study fifteen ribs were used to test the stab marks created
by the five kitchen knives. Each knife was collected from a set of
common kitchen knives, (Brand: Two VonChef knives both
serrated/non serrated and one Rada Cutlery serrated steak knife)
and given a number in order to differentiate the marks. We first
gathering the dimensions of the knives as well as each rib (ribs were
also given a number to identify with). Dr. Misty Weitzel then
generated the stab wounds randomly on the ribs, making note of
which knife was used on which rib for the team to review after the
experiment, and compare results. This was a blind study, including
two rounds of stab wounds in order to strive for more accurate
results. The ribs were boiled in hot water for 1.5 hours to clean the
tissue off the bone. The team examined each rib with the cut marks
and gathered the dimensions of the damage. Using microscopic
measurements, the team used techniques provided by Thompson
and Inglis (2009), to determine the individual knife that inflicted the
wound. Measurements included length, width, kerf damage, and a
general description of the damage. The fracture pattern of the cut
mark was also examined. This is due to the fact that you can also
determine the weapon used with an in-depth analysis of the fracture
patterns. Results of the examination were recorded in the table
under the “results” section.
Forensic anthropologists are becoming better at identifying the type
of weapon used in a crime scene investigation. One of the many
skills forensic anthropologists have is to determine the cause of
death through identifying the magnitude of sharp force trauma.
According to the FBI’s Uniform Crime Report, in 2014 over 1,500
people were killed by sharp force trauma with sharp cutting objects.
Forensic Pathologist, Dr. Joseph Prahlow, has determined three
different types of wounds found in sharp force trauma. They are
stab, incise, and chop wounds. In our experiment we focused on
stab marks left in the bone. Previous work has focused on
interpreting sharp force trauma from bone in order to determine the
cause of death in both forensic and archaeological contexts
(Thompson and Inglis 2009). Currently forensic anthropologists are
typically asked to determine the type of weapon used that produced
a sharp force trauma defect in the bone, rather than match the
morphology of a defect to a specific weapon (Crowder 2009).
Bone often preserves the evidence of sharp force trauma much
longer than the soft tissues (Thompson and Inglis 2009). Cut marks
can be seen by the naked eye, however microscopes have proven
to be better at analyzing the cut marks (Thompson and Inglis 2009).
The evidence of cut marks in the bone may provide a clue to
investigators in identifying the weapon used. Therefore
understanding the differences between serrated and non-serrated
cut marks in the bone will lead forensic pathologists and
investigators to not only determine the type of weapon, but also
guide them to the specific weapon. The purpose of this research is
to measure stab wounds inflicted by a third party on the ribs of a
domestic pig, and identify them as either serrated or non-serrated.
Results
Table 1. Stab mark observations from the naked eye. Kerf damage:
a subjective five-point scale ranging from zero (no damage) to five
(extensive damage) as defined by Thompson and Inglis (2009).
Rib
No.
1 No trauma observed.
2
3
4
5
6
Length
(mm)
N/A
Width
(mm)
N/A
Single shallow fracture located on the anterior side of the costal
3.0
< 0.5
neck.
Small puncture trauma located on the posterior-proximal side of the
2.5
0.5
costal shaft.
Single shallow fracture located on the anterior-proximal side of the
4.5
< 0.5
costal shaft.
Single interrupted fracture located on the superior-proximal side of
12.5
0.5
the costal shaft.
Three fractures with varying traits:
Fracture Fracture
1. Interrupted deep fracture starting on the superior-anterior and
#
#
ending on the superior-posterior side of the costal neck.
1- 24.0
1- 0.5
2. Single shallow fracture located on the superior side of the costal 2- 11.5 2- < 0.5
shaft at the midline.
3- 13.0
3- 1.5
3. Deep fracture located on the superior-distal side of the costal
shaft with a small parallel fracture on the posterior end.
Kerf
Damage
N/A
1
2
1
Fracture
#
1- 3
2- 1
3- 3
Two fractures with varying traits:
1. Single shallow fracture located on the superior-anterior side of
the costal shaft at the midline.
2. Single deep fracture located on the superior-distal side of the
costal shaft.
Fracture Fracture
#
#
1- 2.0
1- < 0.5
2- 7.5
2- 0.5
Fracture
#
1- 1
2- 2
8
Three fractures with varying traits:
1. Single shallow fracture located on the superior-posterior side of
the costal shaft.
2. Small puncture trauma located on the posterior side of the
costal shaft at the midline.
3. Single deep fracture located on the inferior-posterior side of the
costal shaft.
Fracture Fracture
#
#
1- 6.0
1- < 0.5
2- 2.0
2- 1.5
3- 4.0
3-1.0
Fracture
#
1- 1
2- 3
3- 2
9
No trauma observed.
N/A
N/A
N/A
10
No trauma observed.
N/A
N/A
N/A
11
Single deep fracture located on the superior side of the costal shaft
at the midline.
Two shallow parallel fractures located on the posterior side of the
costal shaft.
5.5
1
3
14
No trauma observed.
N/A
N/A
N/A
15
No trauma observed.
N/A
N/A
N/A
13
Fracture Fracture
#
#
1- 3.0
1- < 0.5
2- 1.5
2- 0.5
Three fractures with varying traits:
Fracture Fracture
1. Single shallow fracture located on the superior side of the costal
#
#
shaft at the midline.
1- 2.0
1- 0.5
2. Single deep fracture located on the superior-distal end of the
2- 5.5
2- 1.0
costal shaft.
3- 6.5
3- 0.5
3. Single shallow fracture located on the inferior side of the costal
shaft at the midline.
Discussion / Conclusion
2
7
12
. Figure 1. Significant soft tissue trauma observed between ribs
#10 and #11 with minimal sharp force fractures apparent once soft
tissue was removed
Observations
Fracture
#
1- 1
2- 2
Fracture
#
1- 1
2- 3
3- 1
While the initial purpose of this study was to determine the accuracy
of identifying sharp-force trauma as having originated from either
serrated or non-serrated blades, as defined by Thompson and Inglis
(2009), the results ended up revealing an unforeseen conclusion.
Due to several mechanical issues on the day of data collection,
length and width measurements had to be estimated and fracture
patterns were unable to be observed at a microscopic level.
Because of these limitations, calculating the accuracy of techniques
used in differentiating knife characteristics was impossible. Instead
an interesting factor became evident in comparing soft tissue trauma
to the damage inflicted on the individual ribs.
As apparent in Figure 1, many of the stab marks initially impacted
the bone, but then took the path of least resistance through the soft
tissue into what would be the chest cavity in a live subject. This left a
minimal amount of visible trauma on the bone itself, observed
predominantly as shallow linear fractures, which did not indicate the
possible magnitude of corresponding soft tissue injury. It could be
deduced that in some situations, while skeletal sharp-force trauma
may appear to be low, the associated soft tissue damage could be
much greater, potentially even fatal. Further studies could examine
this phenomenon by using complete specimens in testing, with the
goal of measuring damage inflicted on organs and the vascular
system. Findings would provide a crucial understanding of sharpforce trauma that could prevent a mistaken dismissal of possible
causes of death in a forensic investigation of skeletal remains.
References
Thompson J. Inglis,“Differentiation of serrated and non-serrated
blades from stab marks in bone” (2009): 129-35.
Christian Crowder et al. “Microscopic Analysis of Sharp Force
Trauma in Bone and Cartilage: A Validation Study” (2009): 3-7
Joseph A Prahlow, “Forensic Autopsy of Sharp Force Injuries,”
(2014): 1-2.
Figure 2. Rib #10 showed no apparent damage and
Rib #11 had short fracture on inferior surface.