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Back Spatter from Gunshot Injuries
Back spatter can also travel down the barrel!
There are basically two types of blood spatter; forward and back. Notice I didn’t say “splatter“. Blood spatter is caused when an object impacts a body and forces the blood to break up into smaller droplets. The majority of these droplets are then projected either forward (with direction of force) or backward (opposite the direction of force) essentially. Generally speaking, there is more forward spatter than back spatter in an incident and the blood will disperse in a “cone effect”. The amount of back spatter is dependent on both the energy of the impact and the amount of blood already present at the impact site. For example, a gunshot can create back spatter even when there is no preceding injury. This is influenced by other factors too though. Clothing can “trap” much of the back spatter depending on the type and layers of clothing and location of the wound. If the wound area is not covered with clothing (like the head) then you can see more back spatter. CSIs commonly see some degree of back spatter on the shooting hand in gunshot suicides with head wounds.
The degree of back spatter on the subject varies wildly though. A number of factors influence the deposition of the blood such as subject and victim body positions, wound position relative to subject, distance between subject and wound, the amount of energy causing the spatter, intervening objects (like shooting through a window), and the presence or absence of blood at the impact site just to name a few! The size of the resulting blood droplets varies too. Gunshots and explosions can produce very tiny droplets (with a diameter of 1mm or less) while other impact events can produce larger droplets from 2mm up to 10mm and even larger. You may find back spatter on hands, faces, ears, hair, clothing, weapons, furniture, or practically anywhere near the impact event. It can even be found on items that have been moved to another room (as in a staging). With gunshots, you may find spatter up to four feet from the impact site. In theory, you could find them even further away if there is sufficient air current such as high wind or even the close proximity of a fan.
So how would you use this in a novel? Back spatter can be washed from hands and clothing or even the victim (think of a dog or cat licking the victim). Tiny spatter is very difficult to see however. You could easily have a detective, spouse, or dry cleaner find these tiny spots on a garment, vehicle seat, or window blinds. If on clothing, consider putting the spatter on something like socks, undershirt, or underwear that would have been covered during the suspect’s version of events (or denial of events). That not only places them at the scene but could also place them in a state of undress at the time of blood loss. You get the picture. Be creative and use your imagination to produce a big plot twist.
Free-falling bullets
There is an age old tradition in some cultures to fire celebratory shots into the air on certain anniversaries, events (weddings), or accidents. In the United States this activity seems more concentrated around our Independence day and New Year’s Eve (although pretty rare overall). For the purposes of this posting we’ll just consider bullets fired from small arms as opposed to artillery shells. Bullets falling from the sky are no laughing matter. They can cause serious injury including death. But, there are some misconceptions surrounding the lethality and velocity of bullets returning to Earth.
One of the most common misconceptions is that small arms bullets will return to the ground at the same, or greater, velocity than when emerging from the muzzle of the weapon. Now bullets come in a variety of sizes (caliber) and shapes. Basically they are conical in shape but the nose can be flattened or rounded as can the base (to a lesser degree). Believe it or not a number of studies have been conducted on this issue since at least the early twentieth century. It was found that some common rifle calibers such as the .30-06 attained a muzzle velocity of 2700 feet per second and gained an elevation of 9,000 feet. When a bullet is fired straight up into the air it will continue on it’s flight path until it is overtaken by gravity and begins to free-fall back to Earth.
During this fall the bullet will be affected by air resistance. Now it is theoretically possible the bullet can return one of three ways; nose first, base first, or tumbling. Of the three, a nose first return from a near-vertical trajectory is the least likely. It is much more likely that the bullet will tumble or fall back in generally the same orientation (so base first) especially if it retains any of the gyroscopic spin imparted from the barrel (rifling). Tumbling creates the greatest amount of air resistance so the bullet’s terminal velocity will be lowest in this condition. Regardless, most lead core bullets will return to the Earth in about 45-55 seconds. The falling velocity will be determined by a number of factors including the air resistance and bullet weight. Generally speaking, a smaller bullet like a .22 short will have a lower free falling velocity than a larger one like a .30-06.
While the muzzle velocity for most small arms can average around 1,000 feet per second that same bullet may only reach a free-falling velocity of 150-250 feet per second. If you consider that a bullet needs to reach a velocity of approximately 200-330 feet per second to perforate human skin in a nose first orientation you can see how these falling bullets may not cause a fatal wound. The key words being “may not”. There are plenty of case studies of people being killed by downward arching bullets (though some are not at near vertical falling angles. They can still be very dangerous and cause serious injury. They will typically cause less trauma than one fired at close range however.
Reconstructing the original trajectory is nearly impossible because of all the conditions (wind, air resistance, tumbling, original load conditions, etc.) during flight that can alter the bullet path. So if you are thinking about using a falling bullet in your novel you might want to keep some of this in mind. A falling bullet might only pierce the skin or in some cases just create a bruise. In other cases it may actually cause death. The important thing to remember is that they are not traveling at the manufacturer’s listed muzzle velocity. It should go without saying that you should never attempt to conduct this type of research or experiment. All of the published studies I am aware of were conducted by the military on large scale controlled firing ranges. Do not try.
Future Forensics: The Problem with Biometric Guns
If you haven’t had a chance to see the latest Bond film Skyfall I highly recommend it. If you have seen it then you’re familiar with the concept of a biometric gun (also called a “smart gun”). The idea has been around for a while but, essentially, it’s a weapon that requires a biometric (finger/palm print) scan and match from the owner in order for it to fire (other concepts include RFID chips and magnetic release). This is supposed to prevent another person from firing the gun and the idea has run the rounds in the gun control circles. It’s a swell idea on paper but, in real life it’s much more problematic. Since it appears in a mega-blockbuster I thought you might want to keep a few things in mind should you choose to include a biometric gun in your next novel.
For law abiding citizens, a gun is a tool for self defense (sport too but that’s another topic for another day). When using a gun for self defense, simplicity of operation is preferred. The more complicated the system the more likely there will be a failure. All of us can conjure up images (from movies or television) of a crime victim grabbing a gun at the last possible second and shooting the bad guy. That may not be possible with a biometric gun due to a number of factors which I will separate into electronic, environmental, and situational categories.
First the electronics. Basically you have a digital scanner that reads the friction ridge skin pattern and compares it to the image on file. Then it has to determine a “match” before engaging the mechanical side of the gun to allow it to function. How long does this process take? How about in freezing weather? After being submerged? We’ve all had our laptop “freeze” up on us. It’s annoying but, we’re not fighting for our lives. Presumably the biometric gun operates with a battery of some type. Batteries can drain quickly in cold weather (ask any CSI about using a camera in a blizzard) and fail completely when wet. There are also concerns about impact damage. If the gun drops to the ground will the scanner crack? Will there be internal damage to the circuitry? When your life is at stake every second counts and you need a dependable mechanical weapon.
Aside form the electronics there are serious concerns about the “environment”. A biometric weapon requires a “clean” scan of the finger/palm print. Anything that interferes with the scanning will prevent the weapon from being fired. That means you can’t wear gloves (so much for cold weather use). Violent encounters/attacks also may result in bloodshed. If your hands are bloody then you can’t use the gun. Same goes for mud/dirt, grease, clothing, even water (firing underwater) may be problematic. One also presumes you have to have a flat even contact between your gun and skin which isn’t always possible. Hands can get cut open in a fight (defensive wounds) and the damaged friction ridge skin may not be recognized by the scanner. When you’re in a fight for your life you can get bloody, muddy, etc. and a finicky gun may cost you your life.
Lastly there are situational considerations. Imagine you’re in a public place when a bad guy comes in shooting. You get hit and go down injured. Your gun falls from your hand and a stranger picks it up as the bad guy advances on you. The stranger points your biometric gun at the bad guy, determined to save your life and his, pulls the trigger and…nothing. Well, not nothing. Presumably you’ll both be shot in a few seconds but you get my point. What if the guy that goes down is a police officer and you’re the by stander? Most likely the biometric gun won’t be “coded” to other friends and family and certainly not to a stranger yet, those may be the very people in a position to save your life or that of another.
So if you plan on using a biometric gun in your novel keep some of these things in mind. Gunfights are usually over in a few seconds. Of course, any one of these issues can add tension and danger to your plot line so feel free to use them. I can see your heroine trying to tear off her gloves as the rapist chases her through the park at midnight. Will she get them off before he catches her? Of course my heroine Sarah Richards will have a Glock so it won’t be an issue for her but, it might be an interesting challenge for your characters.
What Happens When Cartridges Burn?
From time to time I get questions about what happens to cartridges when they are exposed to fire. Some people mistakenly believe that cartridges exposed to fire will explode and project the bullet as if it were in a firearm. This is not the case (unless the cooked off cartridge is actually chambered in the firearm at the time of the fire. Even in such events the firearm will not cycle another round (in semi-auto weapons) because there isn’t anything bracing the firearm during blow back. Hollywood has taken quite a bit of license when depicting these events so I thought you might enjoy this (rather long) video showing what actually happens when cartridges are exposed to a number of fire events. Fire fighters have to deal with all kinds of hazards when fighting fires but retail ammunition is not nearly as dangerous as other hazards even though it does sound terrifying when it goes off. After watching the video I was wondering about the first experiment with the custom mount for the cartridges. I wonder if “anchoring” one end of the cartridge actually intensified the reaction because it restricts movement of the cartridge.
Camouflaged Weapons
Camouflaged weapons can be a real nightmare for police officers and CSIs alike. These are weapons that are “hidden” or concealed in some common or non-threatening object. Some common “commercial” products over the years have been things like the pen knife, cane sword, or the pen gun. Edged weapons (knives and swords) are one thing but camouflaged firearms are a whole other danger. Thankfully they are pretty rare among criminals and most sales of legitimate items are to collectors. One main reason for this is that these weapons usually only fire a single shot. That’s not too useful to your average criminal. Another reason is that it takes some skill (and time) to build these weapons even if converted from a legitimate product (like a pen). Still, it happens. I once saw a case of a motorcycle that had been modified to fire a single shotgun slug from the handlebar grip. The idea being that as an officer approached (roadside) the criminal could aim and discharge at close range. This is one reason officers are encouraged to approach motorcycles from the curb side (the handle/throttle is more difficult to modify on that side).
In the video below we see an example of a toy gun that was modified to fire a single shotgun shell. The selection of the modified weapon is important to note for fiction writers. Toy guns like the Super-soaker are designed to look like toys. These toys are very common in the United States and most officers with kids have probably been “attacked” with one on a daily basis in the summer. That is what makes this weapon so dangerous. An individual armed with this camouflaged weapon could approach anyone (even an officer) without raising an alarm. Who could blame them? It’s a matter of conditioning. I think if you ask most police about concerns they may have with toy guns it would be the ones that are designed to look and feel like the real thing. Every cop has nightmares about shooting some innocent kid armed with one of these; but a Super-soaker?
As authors, we try to conceal plots, motives, and identities within the fabric of the story we weave. Surprise is a wonderful mechanism to keep your reader engaged. In the real world these weapons can be deadly but in a novel they can cause a lot of nail biting tension. Readers don’t want everything in plain sight. They expect a little mystery and camouflaged weapons might be one of the tools you can use to give them what they want.
Accidental Discharge: The Sympathetic Response
Note how the finger rests against the frame, not the trigger
Occasionally, CSIs have to respond to scenes where someone has accidentally discharged a firearm. Fortunately it’s not that often. Sometimes the victim offers colorful excuses like “I was just cleaning my gun when it went off” but other times they simply don’t practice good safety. The frequency of these mistakes can increase with alcohol, drug use, or surges in adrenalin. It is this last condition that most often causes police officers to accidentally discharge their weapons. That’s because arrests, especially after a foot chase, can be extremely stressful and cause an adrenalin rush. This reaction is called a sympathetic response. The human sympathetic nervous system is tied directly with our “fight or flight” instincts. This is important for writers because these responses are commonly encountered in high-octane thrillers and crime dramas.
This reaction can also happen when one hears gunfire. Imagine you are a police officer. You and your partner have someone at gunpoint when suddenly your partner shoots. It is possible to involuntarily jerk the trigger and fire your weapon as well following the sound of gunfire. This is one reason you don’t see police and military with their fingers on the trigger until they are ready to shoot. You can always spot an inexperienced shooter if they place their finger on the trigger while just holding the gun or moving through a scene. A good officer will rest his/her finger along the frame (side) of the weapon, never on the trigger.
Accidental discharges can also occur when an officer is either removing or replacing their weapon in the holster. When this happens the gun often discharges downwards. If the officer is lucky the bullet will embed in the ground. If not, they may get a bullet wound in the lower leg or foot. The below video shows a DEA agent who mishandles a firearms during a presentation to school kids and shoots himself in the foot right in the middle of the classroom! Now imagine that happens in your crime scene or in front of the media! It’s a very serious accident but as authors you can use this information to add some drama to a scene. During my career I kept expended bullets I found in the police parking lot walking from my car to my office. I found a total of four in five years. That means that at least four times someone discharged their weapon in the police parking lot accidentally and apparently never got caught. Kind of makes you think a little huh? What if an officer does this at a crime scene but never reports it out of embarrassment? I doubt this would happen in real life but a novel? What challenges would that potentially pose for your characters? How would they explain that “extra” bullet hole and bullet (especially if the officer collects the expended cartridge casing)?
History of Forensics: Murder & the Metal Detector
Searching a stream with a modern metal detector
Necessity is the mother of invention. In 1881 assassin Charles Guiteau fired two shots at the 20th President of the United States James A., Garfield. One of the bullets lodged in his body and did not exit. President Garfield was rushed to the hospital where he lived for 80 days before his death. Doctors were hesitant to do surgery because they couldn’t determine where the bullet was lodged. Famed inventor Alexander Graham Bell learned of the President’s injury and the inability to locate the bullet. He set about to develop a device to “see” the bullet through the skin. Bell developed a coiled detector and performed several successful experiments on finding bullets in animals (sheep) before rushing to the hospital. His first attempts to use the detector were unsuccessful so Bell went back to his laboratory and made several adjustments. Returning to the hospital he tried again without success.
Following the President’s death from his condition Bell went to the autopsy with his metal detector and it worked very well. Some historians believe that a new invention owned by President Garfield interfered with the operation of the new metal detector. What was the new invention you ask…the coil spring mattress. The metal coils essentially “overloaded” or “masked” the signature of the bullet making it invisible. Modern investigators often run into the same problem when searching ground littered with metal trash. The difference is that modern CSIs are very aware of this cancellation. Modern metal detectors can actually be “tuned” to ignore certain signatures and limit their sensitivity to that of the evidence being searched for. I’ll need to do a future posting on modern metal detectors and their capabilities. Being a new invention however, Bell was totally unaware of the coil springs in the mattress and apparently didn’t account for them. Think of it. Two brand new inventions cancelling each other out. It was an unfortunate incident but both inventions continue to enrich our lives.
Future Forensics: Smart Bullet Finds Target at Over a Mile Away!
Here is an interesting story and video about a revolutionary bullet being designed like a cruise missile. When the cartridge is fired the bullet sprouts fins which control it’s flight path to the target. I doubt police will have to deal with this technology anytime soon but it opens up some interesting ideas for a science fiction crime story. The current technology is cool enough but what if your bullet actually “scented” the target like a bloodhound? I’ve written about the amazing capacity of bloodhounds in tracking human scent here and here. But what if a bullet could “scoop up” and analyze scent as a means of finding a target? Bloodhounds do it and scientists have used instruments for high volume air sample screening in atmospheric and environmental studies for years. By analyzing scent could a bullet be programmed to follow a person’s scnet or DNA which is constantly being shed in the form of skin cells. Could you literally pick a person out of a crowd?
Taking it one step further (and this is way out there but we’re talking science fiction) what if a bullet could be programmed to ignore “friendly” targets? That population of “friendlies” may be as small as family members or as large as a military division. Of course, a bullet can’t stop in mid air (or can it) and course corrections at 1100 ft/sec become increasingly difficult if not impossible as the range to target decreases but again, we’re talking fiction. This technology might be something to consider using in your science fiction novel under certain circumstances where you wouldn’t run into certain problems like crowds of people.
Another consideration is the purpose of the projectile. Maybe in your story it is designed for “tagging” or less-lethal incapacitation than it is for killing. In any event, I thought it was interesting and it got my mental gears engaged.
Taser AFID Tags
The Taser has become an invaluable tool in law enforcement; as prevalent as handcuffs and a side-arm on the patrolman’s duty belt. The less lethal control device has undoubtedly saved lives and prevented the kinds of injuries sustained by combative subjects in decades past. When the officer shoots the Taser two probes are launched from the cartridge and once embedded under the skin will temporarily incapacitate the subject by introducing a pulsed current.
Anti-felon Identification Tags (AFIDs) are small serialized confetti-like discs packed into each taser cartridge (the piece that houses the probes that are launched toward the subject). Each cartridge contains between 20 and 40 tags and the alphanumeric serial number on each tags corresponds to the serialized cartridge issued to the officer. In normal light the tabs are colored pink, yellow, and even translucent. But the tags have another useful feature; they are visible under ultra-violet light making them easy for CSIs to find at the shooting scene. AFID tags were introduced to provide some accountability of which Taser was fired in which relative position at a shooting scene. In some ways this evidence is similar to an analysis of fired cartridge cases. A recent study indicated that 75% of these tabs will be found within a 120 sq. ft. area in the direction of fire. That may seem like a large area but it is basically 12 feet in front of the shooter and about 5 feet on either side of the center-shooting line. Having said that, there is no defined “pattern” of distribution as this can be affected by many of the same conditions affecting expended cartridge cases.
AFID Tags in Normal Light
AFID Tags Under Ultra-violet Light
So how are these tags used in an investigation? First, they help confirm the relative position of the deployed Taser. If officer X says he was taking cover behind a door and fired from that position we should find AFID tags in that general area. If the tags are from another officer’s Taser then the officers have to explain that. In high stress scenarios some officers can’t remember exactly where they were when they deployed a Taser, especially if additional use of force methods (such as shooting), chasing, or extensive searching occurs. They also help to show how many officers fired their Tasers at a given scene. These tags are durable and can be found days and weeks after deployment. Many agencies have a policy stating that officers are required to collect the spent cartridge and a sample of the tabs at the crime scene.
So how can you use this information in a novel? Well, most criminals probably don’t know about these tags. Imagine a scenario in which an officer’s Taser is stolen. Days later it is used to commit a crime and the suspect unwittingly leaves behind these tags. The CSIs investigating the scene are now able to link the two crimes together which may provide a clue as to the suspect’s identity. It could be any number of people who could have had access to the officer’s Taser or they may have lost it in a scuffle. Use your imagination and consider an unusual suspect.
The Value of Firearm Ejection Patterns
White tent placards showing shell casing locations
A lot of researchers have studied what examiners refer to as “ejection patterns”. This is the arrangement and dispersion of fired cartridge casings found at a crime scene. The theory is pretty straight forward; cartridge casings will be ejected from a firearm in a predictable manner that will provide insight into the shooter’s position when firing. Unfortunately, the chaism between theory and reality can get pretty wide. Semi-automatic, or self-loading, firearms are designed to extract and eject fired cartridge cases to make room for the next live cartridge in the magazine. Most modern firearms are designed for right-handed shooters and will eject the cases to the rear and right of the shooter. Having said that there are some weapons designed for left hand shooters which eject to the left and still others that eject downward out the bottom of the weapon. The key function is to keep the spent casing from hitting the shooter.
The problem with the use of ejection patterns is that there are a lot of things that can and will influence the manner in which the casing comes to a final rest. First, the manner in which the weapon is held during the firing process. If the gun is held “sideways”, sometimes referred to as “gangster style” with the ejection port facing up, the casing will eject differently than if the weapon was held normally with the sights pointing up. The elevation of the weapon is another consideration. Is the person shooting from the hip or shooting with the weapon at eye level (or both)? Then you have to consider the movement and orientation of the shooter. Is the shooter firing straight ahead of them or to their right or left? Are they moving (running and shooting) or are they stationary? You may never know these things with certainty, especially if the weapon isn’t recovered. All of this is bad enough but we haven’t even begun consider the many factors.
Aside from the weapon design and how the shooter fires and moves there is the environment. Is the shooting indoors? If so, the casings may be hitting other objects like walls, furniture, chandeliers, etc. that can alter the “flight path” of the casing. If the shooter is outdoors are there over-hanging branches from a tree? Is there a strong wind? We also have to consider the surface the casing lands on. Surfaces like snow or a lush green lawn may help to “catch” the casing and allow for very little movement. Other surfaces like cement, linoleum, or tile may allow the casing to “bounce” and change direction. Then there is the slope of the surface. Envision a casing that hits a roadway versus one that hits on the sloped area of the sidewalk leading to the gutter. Think of a cartridge casing like a little football. We all know how unpredictable a bouncing path for a football can be right? Well, casings can act in a similar manner.
When all of that is said and done we still have to consider any “post-shooting” processes that may change the resting position of the expended casing. Cartridge cases are small and can easily be moved if they are kicked, stepped on, driven over, or by other actions. There are a lot of first responders like police, paramedics, medical examiners, even by-standers or family members that may also inadvertently move these casings before the CSI shows up on scene.
The above video shows both slow motion and normal speed ejections. Notice how varied the flight paths are for the same weapon with a static (stationary) shooter. Also, about half-way through the clip you will see one casing actually hit the camera and bounce back towards the shooter.
You might read references to police using ejection patterns in novels or see them on a television show but the analysis is not nearly as straightforward as they might seem. In fact, some studies have shown as much as 25% of casings don’t even eject in the manner or direction as designed. That’s not too surprising actually. Gun manufacturer’s don’t really care about exactly where the casings eject or how consistently they eject in the same manner as long as they stay out of the shooter’s face. Now ejection patterns can provide some general insight into the general location of the shooter but you just have to be very careful about how far you take the reconstruction. So the key is to recognize the many influences that can vary the resting position of the cases. If you want to have some fun with it you could have an expert rely too much on the locations of the casings only to find out later that they had been moved through some other action. That could really throw your analysis into a tailspin.
