Pathology | The Truth About Forensic Science

Interpretation of Gunshot Wounds: Validated Science or Forensic Alchemy

On November 23, 2010, in Autopsy, Ballistics, Crime Scene Investigation, Pathology, by Justin J. McShane

The following is a brief summary of the modern explanation of gunshot wounds according to the proponents of interpreting gunshot wounds (GSW). After you read this, you draw your own conclusions as to whether or not this is empirical or more towards the subjective or non-validated.

Typical GSW explanation in Court

Gunshot Wounds: A summary form a pathology textbook

In general, when a person is shot, the injury sustained will result in a temporary wound cavity that is produced due to cavitation, which occurs when a body moves so quickly in a liquid that the liquid detaches from the body surface. This cavity will only exist for a short period of time after the penetration of the projectile. The size and seriousness of the wound cavity will depend on the amount of energy transmitted by the gun, which is dependent on the length of the barrel; the longer the barrel, the greater velocity.

There are four categories of wounds: (1) contact wounds, which can be hard, loose, angled or incomplete; (2) near contact; (3) intermediate; and (4) distant.

Typical GSW wound interpretation from a pathology treatise

When the wound is a contact wound the muzzle of the gun is placed up against the body at the time of discharge. When this occurs gas, soot, metallic particles, vaporized metal, primer residue, and powder particles can be found in the wound track. Hard contact wounds result from the muzzle being held very tightly against the skin and will create an indent. Due to the closeness of the muzzle to the skin, all the materials from the muzzle will be left directly in the wound which leaves very little external evidence on the skin. If a proper autopsy was conducted soot and un-burnt particles would be found in the wound track. During the autopsy soot could easily be distinguishable from dried blood as soot, unlike dried blood, cannot be removed by either water or hydrogen peroxide. Furthermore, if a dissecting microscope was used, not only would soot always be present in the wound, but also the powder particles left in the wound could be identified.

Where the projectile pierces skin that is tightly flexed over bone, like the skull, the wound will have a different appearance because the gas discharge, which expands between the skin and outer table of the bone, lifts the skin and causes it to “balloon out”. When the stretching of the skin exceeds the elasticity of the skin, the skin will tear. The subsequent size of the tear will depend on the caliber of the weapon used, the amount of gas produced, the firmness of the weapon held to the body, and the elasticity of the skin. This type of tear, however, can also occur when the victim is shot at an intermediate or distant range if the bullet is able to perforate the skin over a bony prominence or curved area of bone that is covered by a thin layer of tightly stretched skin.

Where gas is the cause of the tearing of the skin, however, the detail of the imprint left on the skin will depend on the amount of gas produced from the firing of the gun. The more gas produced, the harder the skin will impact against the muzzle, which results in a greater, more detailed imprint. Imprints cannot only be found on the skin but will be found in the chest and the abdominal region as well because the gas produced will expand in the visceral cavities and adjacent soft tissue causing the chest or abdominal wall to bulge out creating larger imprints which can be twice the actual size of the muzzle.

The presence of a loose contact wound suggests that the muzzle is held in very light contact with the skin as the skin is not indented by the muzzle. In this type of situation, the gas preceding the bullet and the actual bullet itself will be the cause of the indent on the skin. Any soot left on the skin can be easily swiped away but an autopsy can and will reveal particles of powder, vaporized metals, and soot deposited in the wound track, along with carbon monoxide.

: An example of sooting and stippling

In near contact wounds, the second category, clumps of unburned power can pile up on the edges of the entrance wound and on the seared zone of the skin.

The third category, intermediate wounds, are formed when the muzzle is held away from the body at the time of discharge but is still sufficiently close enough that the powder grains from the muzzle can strike the skin and produce powder tattooing, which gets it name from the blackening of the skin around the entrance site caused from the soot. The size and density of these tattoos will depend on the caliber, barrel length, type of propellant powder, and the distance from the muzzle to the target. As the range away from the target increases, the intensity of powder blackening will decrease and the size of the soot pattern area will increase. The powder tattoo which results is unlike the soot in the loose contact wound in that it cannot be swiped away from the skin.

Finally, distant wounds, will be created when the muzzle is sufficiently far from the body so that there is neither deposition of soot nor powder tattooing in the wound track. When a person is shot from a distance, the clothing of that individual will absorb the soot and the powder, thus making it essential for the victim’s clothing to be examined during the autopsy. As the clothing absorbs most, if not all of the soot, the ability of the powder to leave a mark on the skin of the victim will depend on the nature of the material, the number of layers of cloth, and the physical form of the powder.

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Blogger’s comments:

The problem with these types of descriptive groupings lies in the validation. These definitions and descriptions of observable phenomena sounds scientific, but is it? It sounds like something that is empirically based, but is it? How is it possibly measured? How are these conclusions validated? How can we have confidence that these categories and the underlying observations that describe them are unique as to that category and not present in the other categories? We can’t.

Some of the problem comes down to one of the very basics: documentation. Usually in autopsies, photographs are taken. Sometimes they are not taken according to basic principles of photogrammetry. The photos are taken from oblique angles instead of at 90 degrees and most of them have no scaling mechanism. This lack of meaningful photography makes it difficult to verify measurements taken, produce any sort of scale or otherwise reconstruct the wound characteristics. In addition how the investigator approaches documenting the wound can drastically change the interpretation. For example, if one were to clean the wound site or shave it with the idea of revealing it, then gun shot particles, sooting or other characteristics may be removed. In addition, some examiners still use metal rods to try to determine the “path of the bullet” by probing the wound and inserting rods through it. This will deform and alter the organic state of the wound. In the worst case scenario, it can actually create a false path through soft tissue and therefore lead to an erroneous conclusion. Rather than just relying on the typical “I know it when I see it” characteristics outlined above that is used in modern gunshot wound examination, we should use computerized tomography, fluoroscopy and even radiographs including CAT scans.

Head computed tomography (CT) scout image of a patient who suffered a gunshot wound to the head.

$Axial computed tomography image of the chest in a patient with a gunshot wound. Note the comminuted rib fracture (black arrow). A lung contusion is present along the path of the bullet (yellow arrow). A chest tube was placed to treat the right pneumothorax.$

Axial computed tomography image of the chest in a patient with a gunshot wound. Note the comminuted rib fracture (black arrow). A lung contusion is present along the path of the bullet (yellow arrow). A chest tube was placed to treat the right pneumothorax.

A 65-year-old man experienced a gunshot wound to the right frontoparietal region. A CT scan shows that the bullet crossed the midline, lacerated the superior longitudinal sinus, and produced a large midline subdural hematoma. The patient presented with a Glasgow Coma Scale (GCS) score of 4 and died.

Now, after seeing these computerized tomography images, who can argue with what is more persuasive, “I know it when I see it” or the available science?

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Justin J. McShane

Harrisburg DUI attorney Justin J. McShane is the President/CEO of The McShane Firm, LLC - Pennsylvania's top criminal law and DUI law firm. He is the highest rated DUI attorney in PA as rated by Avvo.com. Justin McShane is a double Board certified attorney. He is the first and so far the only Pennsylvania attorney to achieve American Bar Association recognized board certification in DUI defense from the National College for DUI Defense, Inc. He is also a Board Certified Criminal Trial Advocate by the National Board of Trial Advocacy, a Pennsylvania Supreme Court Approved Agency. Justin McShane is the first and so far the only Pennsylvania attorney to achieve American Bar Association recognized board certification in DUI defense from the National College for DUI Defense, Inc.

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What really is Shaken Baby Syndrome? Is it for real?

On November 4, 2010, in Pathology, by Justin J. McShane

I have a daughter. She just turned two. She is the love of my life. She is cute and precious and just absolutely lovable. I cannot imagine what it would be like if she were to die at any age, but especially at this age or younger. I really could not imagine if I or someone else were accused of killing her by way of Shaken Baby Syndrome (“SBS”). Without a doubt there are very few topics that bring out more understandable passion than child abuse or the death of a child. The fact finder, whether it is a Judge or a Jury, does not have the luxury of passion, but is sworn to examine the evidence critically, with skepticism and analytically.

Shaken Baby Syndrome. Is it a valid diagnosis?

The typical case involves an infant, one year old or less, who is seen with respiratory distress at the home, then sent to the hospital. The presentation is typically remarkable with notes of subdural hemorrhages with retinal bleeding, no external trauma and no report of a noteworthy fall.

First let’s talk about the current prosecution-oriented myths that surround Shaken Baby Syndrome. Then, we will employ basic and valid biomechanics and generally accepted principles of anthropometry to reality in order to expose these myths.

Well first, let’s take a look at the “loaded language” inherent in the diagnosis. It is called Shaken Baby Syndrome, which evokes quite a bit of emotion based simply upon its title. However, it is now being reframed as Shaken Baby Impact Syndrome, Non-Accidental Injury Syndrome, and Infant Brain Injury Syndrome to exacerbate the cognitive prejudicial effect of it all.

Anatomical Areas of Concerns in SBS

There are several basic myths that underscore and characterize the situation.

The diagnosis is truly a clinical one and not one that is born of any measure of meaningful empirical testing. The notion that the triad or constellation of injuries together can only manifest based upon violent shaking that is intentional to the exclusion of everything else leads to the potential of extreme mistakes.

Doctors who seek to diagnosis SBS look at several presentation-symptoms during a physical examine to include:
1. subarachnoid hemorrhage. (Arachnoid hemorrhage is blood beneath the arachnoid area of the brain. The bridging vein connects the dural sinus to the cortical surface of the brain);
2. subdural hematoma. (A subdural hematoma is diagnosed when there is bleeding between the dural covering of the brain into the potential space which usually has no bleeding there);
3. patechial retinal hemorrhaging;
4. hypoxia;
5. the lack of lucid interval between alleged shaking and treatment or examination;
6. whether or not the caregiver posits a reasonable explanation according to the treating physician to account for all of this. In other words, does the examining physician believe the caregiver’s explaination for how the damage was sustained?
7. The second myth is that the symptomology cannot present itself from a short distance fall of two to three feet.

According to the prosecution, it is the rotational acceleration of the cranium that ruptures these bridging veins and causes subdural hematoma or subarachnoid bleeding and the retinal bleeding.

Now let’s speak the truth. Is it true that after a short distance fall that presents with no outward trauma that there can never be a subdural hematoma or subarachnoid bleeding and the retinal bleeding with no lucid interval?

Well, no.

The best example of the lucid interval between a short distance fall with subdural hematoma or subarachnoid bleeding and the retinal bleeding with no outward trauma was the case of Natasha Richardson. The untimely and unfortunate death of the famous actress occurred when she was on the “bunny hill” during a very short fall at very low impact resulting in no outward trauma. She remained lucid for quite a while afterwards and then died.

Now let’s use basic anthropometry and basic biomechanics to examine whether or not shaking a baby to cause enough rotational injury resulting in these injuries is indeed even possible without resulting in outward trauma?

12 month old CRABI

Well, again, the answer is no.

The most telling physical realities that confronts Shaken Baby Syndrome and reveals it as an unproven belief or at worst a dangerous myth occurs when one scientifically examines this notion that the only explanation when there is a subdural hematoma or subarachnoid bleeding and the retinal bleeding without outward obvious trauma is SBS. There can, in fact, be subdural hematomas or subarachnoid bleeding and retinal bleeding without outward obvious trauma other than from SBS.

In order to prove this is not unique to SBS or to establish that SBS is indeed impossible without outward trauma, we must first know that scientifically there are generally two different types of force: linear force and translational force. The former is a measure of acceleration that always acts in a particular direction, such as gravity. The latter is a measure of acceleration based upon a rotation. In order for there to be sufficient rotational inertia to cause the intracranial injuries in an infant, according to proponents of Shaken Baby Syndrome, there must be between 6000 to 7000 radians per second squared of rotational acceleration exerted on the cranial cavity.

A peer-reviewed study performed on Penn State Division One football players dispels this as a real possibility. They were given a CRABI device[i] and asked to shake the device as violently as possible with the stated aim for these well-trained athletes to create as much rotational force as possible. At their best, they could only generate approximately 1500 radians per second squared. However, when they were asked to slam the child’s head against a hard object, like a floor, they could generate 50,000 radians per second squared. As the researcher noted with this modified method of slamming the child’s head against the floor, an examining physician would see signs of external trauma. This is basically what we would expect to see if the impulse (J) was low. (J = FΔt; as t (deceleration) gets smaller, the J value drops significantly even when presented with the same force. Small J means the change in momentum is very fast, which is obviously going to have physical ramifications. When the experiment was modified to include a short distance fall, sufficient radians per second squared were created.

12 month old Crabi in short fall

Further the study found that in order for the football players to generate the approximate 1500 radians per second squared, the players instinctively held on to the rib area so strongly that it would very likely cause broken or bruised ribs and/pr a long bone fracture for example in the arm or leg.

Additionally from the world of biomechanics and anthropometry we learn that in an infant the head is a disproportionately large amount of mass as compared to a human with massively underdeveloped neck musculature to support its weight or orientation. This is why we are all taught to hold a baby’s head when picking it up or the head will flop causing injury to the neck. Such is the case with SBS. If it is an alleged SBS situation, the delicate area of a baby’s neck would definitively present to the examining physician with unmistakable signs of trauma.

Additionally, if there is a lack neck injury then there is also less then demonstrable evidence of Shaken Baby Syndrome as the head and the musculature around the neck of an infant is the most vulnerable area involved with babies.

The neck is the most vulnerable area in an infant and will break first before SBS occurs

Other myths that are easily demystified include:

retinal hemorrhaging is exclusive to abuse (N.B., The true mechanism that causes retinal hemorrhaging is not known)
subdural hematomas are a presentation of shaking
retinal bleeding is diagnostic of abuse
it is impossible to have a period of lucidity afterwards
chronic subdural hematomas never re-bleed, meaning if there is a preexisting injury then it always heals and it is never subject to re-presentation (N.B., subdural hematomas cannot be dated)

[i] The Child Restraint/Air Bag Interaction (CRABI) dummy has been developed at First Technology Systems, Inc. (FTSS) to evaluate small child restraint Systems in automotive crash environments, in all directions of impact, with or without air bag interaction. There are three sizes of infant dummies: a 6-month-old, 12-month-old, and 18-month old. Accelerometers are used to measure head, chest acceleration and head angular acceleration.

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