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Category Archives: Firearms Analysis

Forensics For Dummies, 2nd Edition Coming Soon

 

FFD 300X378

 

Just got the new cover for Forensics For Dummies, 2nd Edition.

It will be released from Wiley on 2-29-16

Pre-Order now

 

Fingerprinting Bullets: A New Forensic Science Technique

Bullets recovered from crime scenes or bodies can tell investigators a great deal: the caliber of the weapon can be determined by measuring and/or weighing the bullet; the marks left on the bullet’s surface by the lands and grooves and twists of the barrel can reveal the manufacturer; and these same striations can be used to match the bullet to a particular suspect weapon. These striations area the most individualizing and therefore the most useful in criminal investigations involving forearms.

But what if the bullet is too damaged for such comparisons? All is not lost. An analysis of the chemical make up of the bullet might reveal not only the manufacturer but also the batch from which it came. This might serve to narrow the location of purchase and ultimately lead to the perpetrator..

Bullet Fingerprints To Help Solve Crimes: http://phys.org/news/2014-07-bullet-fingerprints-crimes.html

 

The Writers Forensics Blog: 100 Top Websites to Bookmark

The crew over at FornesicScienceDegrees.org have listed The Writers Forensics Blog as one of their Top 100 Websites to Bookmark, which they describe as a “list of great sites to present practical, real-world information on the subject.” Many great sources here.

Thanks. I’m flattered.

 

 

Undetectable 3D Printed Gun

3D Printed Gun

 

 

Airport security uses low level x-rays and metal detection. But will it detect a plastic gun? Like one that can be printed using the 3D printing technology?

 

3D Printer

3D Printer

 

 

Such a gun was predicted many years ago in Frederick Forsyth’s classic The Day of the Jackal. The original 1973 movie version anyway. The Jackal not only had that cool rifle disguised as crutches, but also a double-barreled handgun that was plastic and fired plastic bullets, if I remember correctly. Been a while since I saw the movie.

 

day of jackal

 

Fast Bullets and Broken Glass

Crime scene reconstruction is an art and a science. If investigators can determine what happened, to whom, when, where, and how, they are well down the road to solving the case. Ballistic trajectories are often part of this analysis.

bullet_holes_in_glass

 

What was a bullet’s direction of travel? Was the gun fired inside the house or outside? Better yet, what was the speed of the bullet? Directionality can refute or support suspect alibis and witness statements and bullet speed can narrow the type of weapon used when the bullet itself is not available.

It has been known for many years the glass fracture patterns can reveal directionality but now there seems to be a method for determining the projectile’s speed. Very cool technology.

 

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From HOWDUNNIT: FORENSICS:

The lab might also be asked to determine how and why a glass object, such as window, fractured. The pattern of the breaks and cracks seen in a window give the examiner a clue as to the speed and direction of the impact; this helps him determine what object likely caused the break. Was the object moving at a low velocity, such as a rock or fi st, or at a higher rate, such as a bullet or explosive shrapnel?

Cracks in windows and other flat plates of glass tend to be radial and concentric.

Radial cracks spread outward from the point of impact in a spoke-like configuration. Concentric cracks are a series of progressively larger circles around the point of impact. Overall, the cracked window might look like a spider web.

Certain characteristics of a break allow the examiner to determine the direction from which the impact came. This can be critically important in crime scene reconstruction. Did the bullet penetrate the window from outside in, or was it fired from within the house? Did a perpetrator break the window and enter, or did someone within the house break the window in an attempt to stage the scene and make a domestic homicide look like a breaking-and-entering murder?

Stress-fracture lines known as conchoidal lines, which radiate away from the impact site (see Figure 15-3), can help make this determination. Viewed through the thickness of the glass, these lines tend to curve out and away from the point of impact. Looking more closely at these conchoidal fractures, smaller lines that radiate in a perpendicular direction from edges that face away from the impact site may be seen. These are called hackle marks.

15-3 Conchordial fracture lines jpeg

Figure 15-3: Conchoidal fracture lines. Conchoidal fracture lines tend to curve out and away from the point of impact. Hackle marks also reveal the direction from which the force was applied.

 

If a projectile such as a bullet strikes a window and penetrates it, but does not completely shatter it, it may leave a hole with or without surrounding fracture lines. On the side of approach, the bullet creates a rather clean hole, while on the opposite side, a small cone-shaped plug of glass is forced out. Simple visual inspection of the impact site reveals the projectile’s direction of travel.

If multiple bullets or other projectiles fracture the glass, it is often possible to determine the order in which they struck. Typically, the radial fractures caused by the second object do not cross those of the first. That is, they end when they encounter glass that is already fractured (see Figure 15-4).

15-4 Intersecting fracture lines jpeg

Figure 15-4: Intersecting fracture lines. Impact radial fracture lines end abruptly at those produced by a previous impact. In this case, fracture B followed fracture A.

 

These findings can be extremely important in corroborating or refuting suspect and witness statements and in reconstructing the events surrounding the crime. They can also be useful in assigning culpability.

Let’s say two gang members decide to do a drive-by shooting of a rival gang member while he is sitting in his car. The driver fires through the victim’s car window and begins to drive away. His accomplice then takes the gun and fires again. Both bullets pass through the window and strike the victim, one in the shoulder and the other in the head, killing him. Since both bullets came from the same gun and both men have gunshot residue on their hands (see Chapter Sixteen: Firearms Examination, “Gunshot Residues”), which of the shooters was the actual killer? Was it the first bullet (the driver) or the second (the passenger)? The dilemma is resolved when analysis of the fracture lines in the victim’s car window reveal that the second bullet was the killing shot.

 

 
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Posted by on June 14, 2013 in Crime Scene, Firearms Analysis

 
 
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