Blog Archives

Ever Wondered if an AK-47 Will Fire Underwater?

I’m a sucker for these types of videos and I figured a few of you might be too.  Some people question whether a gun will fire under water and what the effects might be.  As you’ll see in the below video, the gases released during discharge react differently in water than they do in air but the video does give you some idea of where and how the gases and GSR are expelled from the firearm. Obviously you could never recover GSR from a suspect firing a gun under water but the video is neat nonetheless. I thought it was especially interesting to see the cycling of the weapon was faster under water than in air too. Enjoy.

Laser Mapping a Crime Scene

Leica_ScanStation_P20_PIC_180x180I have been a bit AWOL lately.  Every now and then I need a vacation and this last one turned out to be quite a little adventure. So today I thought it would be interesting to talk about the next generation of crime scene mapping. When I first started crime scene work we used metal tape measures and did our crime scene sketching on large pads of paper. While paper isn’t obsolete, the next generation of crime scene mapping offers many advantages. Tape measures are a pain in the butt. They bend, they come loose, and sooner or later you drag one through a pool of blood (yuck!).

Over the years CSIs have been utilizing various laser based measurement devices. They vary from small hand held range finders (great for inside measurements) to Total stations (like the ones you see surveyors using). Near the top of that list is the automated laser based scanner. These types of units gained international exposure during the reconstruction of the car accident claiming the life of Princess Diana. These units are not in common use yet due to the cost (some in excess of $100,000.00) but more and more agencies are beginning to use them.

The above video demonstrates one such unit from Leica instruments. I’ve used a number of Leica products and found them to be top notch. The scanner is about the size of a small trash can and mounted atop a surveyors tripod. Once activated the unit will bombard the crime scene area (up to a distance of nearly 1000 feet)  with millions of laser pulses which bounce off various surfaces and return to the unit. It will scan a full 360 degrees and 270 degrees above and below the unit. Basically everywhere except the unit location. A typical room can be scanned in a few minutes. CSIs can also link the unit with GPS which is really handy in outdoor crime scenes (especially ones in remote locations). The units can even operate in complete darkness.

Those millions of points create an exact three dimensional map of the scene that can be represented in a rotational diagram. It even records color. Utilizing the scanner software this virtual map allows CSIs to determine distances between any objects in the scene. No more missed measurements and the accuracy is phenomenal. The CSI can also zoom and pan around the image to view evidence from different perspectives. As you can see in the video, certain points can be hyper-linked to crime scene photographs or even text reports. This is a powerful tool for the reconstructionist and can be useful for prosecutors as well.

This is cutting edge stuff and you may want to consider using this technology in your next novel. Remember, this unit will record everything visible to the laser so it may even “find” a piece of evidence missed by your detective. Maybe your scene was mapped at night (dumped body or car accident) and a crucial piece of evidence wasn’t seen by the on scene responders. Then your protagonist can go back and find the crucial clue. Use your imagination and have fun with it!

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.

Crime Lab Tour: The Forensic Garage

Vehicle examination bays are a relatively new feature of the modern crime lab in the United States. Now there have always been garages that vehicles could be sequestered in but that was not their primary purpose. Large agencies may have used parking structures (for patrol vehicles) or impound lots but they lacked certain amenities for the forensic scientist.  When I first got into forensics we used to process vehicles at the tow yard. Some had indoor garages but others did not. In some cases they would back the cars into a kind of shipping container where you couldn’t even open the doors! Another problem is the potential for unauthorized access. Even if you lock the vehicle it’s possible for damage to occur from the normal operations of the tow yard. Workers may brush against the car wiping off fingerprints or they can accidentally hit the vehicle as they move other vehicles around. I’ve even seen cases where the suspect (owner) climbs the fence after hours and literally steals their car back from the tow yard.

A vehicle in a tow yard

A forensic garage offers certain qualities that are hard to find in other facilities such as,

  1. Security from all persons not affiliated with the investigation (including other officers and detectives)
  2. Environmental control (weather, lighting, temperature, etc.)
  3. Access to specialized tools and processing systems.

A vehicle in transit on a flatbed tow truck

Most vehicles can be processed in the field. Fingerprinting a recovered stolen vehicle with no damage may not necessitate it being towed back to the crime lab. If the car was used to kidnap and rape a woman however, it’s going to take time to process.  Some vehicles can take hours to properly search and document. It’s nice to have a safe and secure area to work in where you don’t have to worry about approaching snow storms, security, limitations of your equipment, or even the prying eyes of the media. You may have to wait hours for a search warrant to look for various kinds of trace evidence, documenting damage like impacts or bullet holes, or even restoring obliterated VIN numbers so it nice to know the vehicle is protected.  A forensic garage allows the investigator to control the environment which is critical for things like an ALS examination (light control) or the application of blood reagents like Luminol.

Looking for a bullet with a fiber optic scope

In addition to the controlled environment the garage can provide very specialized equipment such as chemical fume hoods, vehicle lifts, pneumatic tools, even a winch. Vehicle lifts are handy for getting under a vehicle to recover fired bullets, remove tires or bumpers, or even document things like damage to brake or fuel lines. It’s also nice to get under vehicles to look for blood, tissue, or clothing strips in cases of hit and run or homicide where the victim is intentionally run over. You may even find vegetation from the crime scene wedged in the undercarriage. Most garages are designed to be over sized. Large enough to house a city bus or several vehicles at once. Further, the garages are alarmed, can be easily locked down, and may even have video surveillance.  I was recently at a large garage that even had a huge tent structure that allowed the entire vehicle to be fumed with cyanoacrylate! Most forensic garages have room for two to six vehicles although some agencies may have more if they can demonstrate a need (like a regional or state crime lab).

Vehicle on a lift. Notice the chemical fume hood in the corner to the left. These are used for things like fingerprint processing with chemical reagents. The white hose is to evacuate exhaust fumes.

Pink ballistic trajectory rod in a vehicle

Bottom line is that a forensic garage is a unique feature of the modern forensic laboratory. They are nothing like the automotive garages you may be used to. They are over sized to ensure there is enough room for a photographer to be able to get the whole car in a single photograph and some even have cat walks above so elevated pictures can be taken. If you ever get a chance to tour a crime lab call ahead and see if they have a garage you can visit. Some may be off site from the main crime lab so it doesn’t hurt to ask in advance.

A view without a vehicle

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.

Defining Trace Evidence

Pet hairs and fibers in a vehicle

“Trace Evidence” is a term that is commonly used by detectives and forensic scientists but may not be widely understood by others. The term gained prevalence in a series of three papers written by Edmond Locard in 1930 and published in the American Journal of Police Science. The papers define what has become known as the Locard Theory of Exchange. Basically, the theory holds that whenever two things come into contact with one another they will likely leave “traces” of their presence with each other. Imagine a man walking across a muddy field. He leaves behind shoe print impressions and in return the muddy soil will cling to his shoes. That scenario creates an “exchange” between the scene and the suspect. obviously, the more activity and participants in a given crime scene, the greater the potential for such exchange.

I’m not wedded to any particular definition but I think many criminalists would agree that when they think of “trace evidence” they imagine small items normally examined with a microscope. Others might also include impression evidence from shoes and tires but, as an author, you needn’t concern yourself with parsing it all out. I have previously described how criminalists “touch” evidence to minimize any exchange and/or destruction of this valuable evidence. But, detectives rely on this exchange to prove connections between the suspect, victim, and crime scene. As authors you can use various types of trace evidence to drive an investigation and challenge your characters. Trace evidence can be divided into several categories. Here are a few (of many) examples:

Biological:

  • DNA (blood, semen, saliva)
  • Hairs (human, pet, livestock)
  • Fingerprints
  • Stomach contents (vomit)

Physical:

  • Synthetic fibers (clothing, carpet)
  • Paint chips
  • Safe insulation
  • Glass fragments

Natural:

  • Botanical (pollen, seeds, plant fragments)
  • Geological (soil, sand)

I will soon post some articles describing how and where CSIs search for this trace evidence so keep checking back!

Components of a Shotgun Shell

Clockwise from upper left; gunpowder, No. 8 pellets, blue shotcup, and empty 12 gauge shotgun shell

Shotgun shells are similar to center-fire cartridges with one important distinction; the wad or shot cup. Shotgun shells come in a variety of calibers (such as .410, 20 gauge, 12 gauge which are the most common) and typically fire pellets instead of a single projectile. Having said that, there are shells designed to fire a single projectile called a “slug”. The size and number of pellets varies as well and are designed for specific uses.  Size 8 or 9 shot are small BB sized pellets used for target practice and small game hunting while larger shot such as 00Buck are used for home defense and predator hunting.

When a typical cartridge is fired at a crime scene the CSI might look for both the bullet and the cartridge case. The other component (powder) is generally burned up but can be found in a residue. But with a shotgun discharge the CSI may also be looking for the wad or shot cup . Most modern ammunition uses a shotcup which is a plastic “cup” with separate “petals” which fold away after leaving the muzzle and slow its forward movement (see photo). Older shotgun shells commonly used a wad which was a small fibrous disc of the same diameter as the shell. It’s kind of like a little padded sponge but without the holes and denser. Without a wad or shotcup the pellets would exit the muzzle with much les energy because the pellets can’t hold back the pressure as well as a solid projectile. Shotguns are smooth-bore weapons and generally do not have rifling which means the examiner can not do a traditional rifling comparison like they would with an expended bullet.

Various types of fired shotcups

Badguys will sometimes pick up their expended cases or shells (often referred to as “policing your brass”) but finding the shotcup would be very difficult as it can travel quite some distance from the muzzle (I have found them over 100 feet away).  Sometimes, if the muzzle is in contact or close contact with the victim the shotcup or wad may even be recovered from inside the victim at autopsy.  Now a firearms examiner can not link a shotcup to a particular weapon but examining the shotcup might reveal what type and size of shot was used and even the manufacturer of the ammunition. This might be important circumstantial evidence to consider when searching a suspect’s home, vehicle, or financial records.

Expended shotcup on ground

Is That Cordite I Smell?

Not unless your novel is based in a pre-WWI era. This is one of those terminology mistakes that seems to have kept a foot hold in modern crime and suspense thrillers. I’m listening to an audio book during my commute and the NYT best-selling author has referenced the smell of Cordite several times in the modern tale. Perhaps it’s a little thing that a lot of readers may not notice but it is a glaring error to knowledgeable readers. The fact that such a well regarded author (one with a reputation for doing good research) makes this mistake tells me that many other authors may make the same error. Truthfully, it’s a simple error to make but even easier to avoid.

Cordite was a type of smokeless propellant for firearm cartridges developed by the British from the early 1890’s to about the end of WWI when better smokeless powders were developed. It was still used in heavy guns (like tanks) to varying degrees but it is not produced anymore and certainly not for modern firearms. It produces an acrid smell like burnt acetone if you can imagine that. Modern smokeless powders produce a much less noticeable odor. The smell of modern powders don’t “hang in the air” unless you’ve discharged dozens or hundreds of rounds in a confined space. That’s not to say a seasoned CSI or detective couldn’t detect an odor after a few shots were fired but it just wouldn’t be as pungent or last very long (minutes) in most cases.

So if you’re writing a modern novel avoid descriptions like “After emptying his magazine at the knife wielding thug, Butch Big-guns nearly gagged on the curtain of cordite hanging in the air”. You are of course welcome to use the character name Butch Big-guns if so inclined :)

Bullet-Proof Glass Demonstration

This is a really interesting video of a ballistics test on bullet-proof glass designed for vehicles. Technically, these products are really “bullet-resistant” since eventually it can fail (with enough bullets) or some larger calibers and bullet types. Nonetheless, it is interesting. This is obviously done under very controlled conditions with a proven product so it goes without saying DON’T TRY THIS YOURSELF!

Detecting Patched Bullet Holes in Painted Drywall

Some of you know that I continue to conduct research in the forensic sciences so I thought it might be fun to share my latest paper on detecting patched bullet holes with portable x-ray units. I hope you enjoy!

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