Forensic Lecture 5
Firearms are involved in what fraction of suicides?
2/3
Firearms account for for what percentage of U.S. homicides?
60%
What is "Cavitation?"
A cavity that forms from the path of the bullet as it travels through the body.
First gunshot wound seen on x-ray?
A rabbit - seen by Professor Wright
A. What percentage of suicides include multiple gunshot wounds? B. What causes this?
A. 2% B. Faulty ammunition, non-fatal wounds, reflex action, automatic weapons
Majority of contact wounds are often on the _____A.____ side of the head using the ______B._________ hand.
A. Right B. Non-dominant
What are 2 low velocity weapons?
Air guns and small caliber handguns
How are bone and bullet fragments usually distributed?
Along the bullet track within soft tissues and beyond the defect in the bone. They bevel the bone toward the direction of travel.
How does the fragmentation area widen in high-velocity soft point bullets?
Area of fragment deposition widens as the distance from the entry site increases creating a cone shaped distribution with the apex at the entry site
Why are MRIs not used as much as CT even though they establish the course of the bullet through the soft tissue well.
Because MRIs do not show the osseous injuries or the bullet itself.
Why are organs like the liver and brain injured severely by bullets?
Because temporary cavitation may occur, outside of the normal bullet track.
What are the 2 main sizes of the shotguns
Birdshot and Buckshot
Semijacketed =
Bullet Partially encased (open lead at tip designed to deform on impact)
Full metal jacket =
Bullet entirely encased
Hollow-Point Bullets =
Bullets have open cavity at their tips and are designed to deform on impact transforming them into mushroom shape
How are wound tracks identified on images?
By the presence of gas, hemorrhage, bone or metal in a linear distribution.
What metal is most commonly used in metal jackets?
Copper (Other metals like cupronickel and steel are also used)
Caliber is most commonly measured in what?
Decimal of an inch or in mm/
What is the purpose of a metal jacket on Medium and High Velocity bullets?
Metal jackets protect against deforming while in the gun barrel.
True or False: Bullets of MULTIPLE calibers can be present in the same victim.
TRUE
True or False: Correlating the angle and direction of fire with the crime scene may help to recreate the relative positions of the victim and assailant.
TRUE
True or False: Deformation increases tissue damage making the bullets more effective at wounding than non-deforming bullets.
TRUE
True or False: Entrance and Exit wounds are essential for case reconstruction.
TRUE
True or False: Evaluation of bone fragments can determine direction of travel
TRUE
True or False: Fluoroscopy is useful in autopsy for locating bullets and scanning for unsuspected bullets.
TRUE
True or False: For accurate analysis of caliber, two views should be obtained at 90 degree angles.
TRUE
True or False: High-velocity soft point rifle bullets usually show marked fragmentation leading to a "lead snowstorm" appearance.
TRUE
True or False: Higher kinetic energy gives the rifle bullet greater wounding potential than the handgun bullet.
TRUE
True or False: Hollow-point bullets usually mushroom without fragmenting.
TRUE
True or False: If the projectile passes through other objects, for example, the metal door of a vehicle, prior to entering the body, parts of the object may also enter the body and mimic fragmented projectile or bullet jacket
TRUE
True or False: In Shotguns, the size of cartridge is measured in gauge instead of caliber
TRUE
True or False: Instead of a single bullet, shotguns fire multiple pellets or "shots"
TRUE
True or False: It can be surprisingly difficult to determine the number of bullets in a victim
TRUE
True or False: Medium or long range injuries (via a low velocity weapon) may be superficial.
TRUE
True or False: Modern forensic radiology evaluates both fatal and non-fatal wounds.
TRUE
True or False: Presence of prior gunshot wounds may help in identification.
TRUE
True or False: Semi-jacketed, non-jacketed, hollow-point, and soft-point bullets deform (or break apart) on impact.
TRUE
True or False: Shotguns and High-velocity hunting ammunition both leave characteristic appearances.
TRUE
True or False: Small metallic fragments produced when bullet strikes bone and subsequent bone fragments may lead directly to the bullet and clearly indicate the bullet's path.
TRUE
True or False: Temporary cavitation can result in compression and subsequent stretching of the surrounding tissues leading to permanent damage.
TRUE
True or False: The annual number of suicides EXCEEDS the number of murders.
TRUE
True or False: The bullet CAN tumble or rotate around its short axis.
TRUE
True or False: The interpretation of a projectile path may be further complicated in the case of multiple projectiles fired in different directions.
TRUE
True or False: The longer the barrel, the more time for acceleration and the faster the bullet will be when it leaves the gun.
TRUE
True or False: The wounding mechanism is similar for both rifles and handguns.
TRUE
True or False: When a bullet strikes a target, it STOPS spinning.
TRUE
True or False: Wound morphology is often enough to determine the type of wound (along side with gunpowder residue).
TRUE
True or False: Clinicians are notoriously bad at analyzing entrance and exit wounds,
TRUE (Ex: 75% of multiple gunshot wounds were interpreted incorrectly in one study)
True or False: Steel and lead pellets can usually be distinguished from one another at radiography
TRUE (Lead pellets tend to be deformed and fragmented by impact with soft tissues and bone whereas steel shot usually remains round)
True or False: Caliber does NOT address the weight of a bullet or size of the charge.
TRUE (this measurement is important in determining kinetic energy)
True or False: Subcutaneous tissues offer path of least resistance and bullets may fail to penetrate the fascia (concerning low-velocity weapons)
TRUE (Phenomenon is most common when the entry wound is at a shallow angle to the skin surface)
Yawing refers to:
The bullet twisting while in the body causing greater damage
Earliest human gunshot wound?
King Charles XII of Sweden in 1718
Weight of bullet in GRAINs
1 ounce = 437.5 grains
Ratio of Fatal homicides to non-fatal homicides.
1/700
What body parts are targets in suicides by gunshot?
Head Chest Abdomen
True or False: Bullets change trajectory especially when contacting bone.
TRUE
What are the Benefits of CT?
1. 3D reconstructed images can be created and turned during the autopsy 2. Can differentiate other foreign objects from bullets based on Hounsfield Units
What are the 3 general classifications of gunshot wounds and what do they involve?
1. Abrasion (Involves graze wounds and can be mistaken for classic abrasion from blunt trauma.) 2. Penetration (Bullet strikes and enters body without exiting) 3. Perforation (Bullet strikes and enters the body, then EXITS the body)
4 Components of a bullet
1. Bullet (normally lead) 2. Charge (flammable propellant) 3. Cartridge case (contains the Charge) 4. Primer (ignites the charge)
What are the major types of firearms and what do they fire?
1. Handguns-Bullets 2. Rifles- Bullets 3. Shotguns - Small pellets called "Shot"
What are the three types of Ballistics, and what do they each involve?
1. Internal (motion WITHIN the firearm) 2. External (Motion in the AIR) 3. Terminal (Effect of the projectile hitting the target)
What factors are important in "Postmortem Radiology"?
1. Locating the projectile 2. Depicting the bullet track 3. Used to ID the type of ammunition and weapon 4. Facilitates retrieval of bullet 5. Uses Radiographs, Fluoroscopy and CT
Shotgun pellets/shots emerge in a mass that disperses into a pattern determined by what 3 factors?
1. Range 2. Barrel length 3. Degree of "choke" or constriction of the bore at the muzzle
Caliber measures what?
Diameter of the bullet
True or False: Deformation of the bullet on impact does NOT affect its tendency to tumble.
FALSE
True or False: Entrance wounds in the skin CAN be used to determine caliber
FALSE
True or False: Low velocity weapons have HIGHER wounding potential.
FALSE
True or False: The U.S. has the LOWEST rate of homicide
FALSE
True or False: Wounds to the mouth often INVOLVE the tongue or teeth.
FALSE
True or False: it is okay to "eyeball" the bullet caliber on the radiographs
FALSE
True or False: the type of metal used in the jacket of a jacketed bullet CAN be determined from radiographs.
FALSE (Because bullet jackets are occasionally made of steel, it may not be appropriate to place a bullet wound victim into an MR imager when the nature of the bullet construction is unknown)
True or False: After creating a mushroom shape on impact, bullets ACCELERATE faster and deliver energy to a smaller volume of tissue.
FALSE (Bullets DECELERATE faster)
True or False: The location of the bullet is always clear from the entrance and exit wounds.
FALSE (It is not clear)
True or False: Wound Ballistics is a subset of EXTERNAL Ballistics.
FALSE (Subset of TERMINAL Ballistics)
True or False: Shotgun injuries resemble rifle and handgun wounds
FALSE (They differ substantially)
True or False: Shotguns do not have rifled barrels but their pellets still spin
FALSE (They do NOT spin)
True or False: The higher the shotgun gauge, the BIGGER the diameter.
FALSE (the SMALLER the diameter)
True or False: Rifle bullets leave the gun at a much LOWER velocity than handgun bullets.
FALSE (HIGHER velocity caused by the longer barrels of the rifles.)
True or False: Full metal jacketed bullets do NOT remain in one piece and show SIGNIFICANT deformation.
FALSE. (they remain jacketed and do NOT show sig. deformation unless they strike bone)
What elements are NON-MRI compatible?
Ferromagnetic elements such as 1. Cobalt 2. Nickel 3. Iron
Bullets take on a ___________ shape when they deform on impact.
Mushroom
What is "Rifling" and what does it do?
Rifling = Spiral grooves within the barrel of a gun that grip the bullet and cause it to spin along its long axis.
How does spinning via rifling help the bullet's path?
Spinning creates a gyroscopic effect which gives the bullet more stability resulting in a straighter course with more accuracy.
Although in the past all shotgun pellets were made of lead, due to recent wildlife regulations what are shotgun pellets used on waterfowl made of?
Steel
THV (tres haute vitesse, very high speed) bullet, which was originally produced in _____A______ & used by the police. It is intended to be _____B____-weight, high-velocity ammunition. The conical point allows easy penetration, even of soft body armour and the abrupt _____C_______ slows it down suddenly, stopping the bullet within its target, preventing injury to bystanders
THV (tres haute vitesse, very high speed) bullet, which was originally produced in FRANCE & used by the police. It is intended to be LIGHT-weight, high-velocity ammunition. The conical point allows easy penetration, even of soft body armour and the abrupt WIDENING slows it down suddenly, stopping the bullet within its target, preventing injury to bystanders
True or False: A bullet may end up pointing TOWARDS its entry wound and may point AWAY from its direction of entry due to tumbling.
TRUE
True or False: A discrepancy may lead to a search for bullets at the scene.
TRUE
True or False: Accurate knowledge of focal-spot to bullet distance, and bullet to film distance, caliber can be calculated based on a formula
TRUE
True or False: Bullet fragmentation depends on construction of the bullet.
TRUE
True or False: Bullet injuries are most severe in friable organs like the liver and brain.
TRUE
True or False: Bullets are usually classified by caliber
TRUE
True or False: Bullets can enter a wound that was made previously and other metallic densities may be confused with bullets.
TRUE
What does Temporary Cavitation involve?
The rapid rebound of the tissue after the bullet passes through the body
What is "Ballistics?"
The study of projectile motion
What determines a bullet's wounding potential?
Velocity of the bullet and Weight of the bullet
What can be used to determine if a crime has been committed when decomposed bodies are discovered?
X-Rays
Can steel pellets move in an MRI?
Yes because they are Ferromagnetic
Can movement of the bullet occur within tubular structures?
Yes, Ex. Vascular system, bronchial tree, alimentary canal, urinary tract, neural canal. - Bullets fired into the spine may lose velocity abruptly against the strong bone and sink for surprising distances into the subarachnoid space.
What factors modify the migration of missiles?
force and direction of blood flow, gravity and position, pressure changes associated with Valsalva maneuver, variation in vascular anatomy, site of entry, and weight of the projectile.