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Saturday, April 28, 2012

Griekwastad Tragedy – UPDATE (Part 3)


Continued from Part 2

Picture Credit: Maine State Crime Laboratory

As mentioned in the final paragraph of the previous post, there’s a possibility that the  investigations are being delayed due to factors pertaining to the microscopic comparisons of test-bullets with evidence-bullets. This aspect will be dealt with under the heading, "Linking Fired Bullets to Suspect Firearms" - further down in this posting.

THE FINER ASPECTS OF FORENSIC BALLISTICS
(A brief expose)

GLOSSARY OF TERMS:

ENGLISH SYNONYMS AFRIKAANS
Projectile Bullet Koeël, Projectiel
Cartridge case Casing Doppie
Primer Igniter Slagdoppie, Ontsteker
Propellant Gunpowder Kruit
* Cartridge Ammunition Patroon, Ammunisie
Primer residue Gunshot residue Onsteking residu / neerslag
Propellant residue Gunpowder residue Kruit residu / neerslag

*Note : “Cartridge” refers to all the ammunition components collectively, before they are discharged, or detached by other means. Components of a small-arms cartridge: Cartridge case, Primer, Propellant (gunpowder), and Bullet. 


Definition:
Forensic Ballistics is concerned with the scientific and technological analysis of all ballistic related evidence and related phenomenon, with the sole purpose of assisting the criminal justice system in establishing the true facts in a particular case.

Ballistic Related Evidence:
Ballistic related evidence collected at murder scenes includes, among other things, firearms, fired bullets, fired cartridge cases, as well as a variety of chemical compounds commonly known as “propellant-powder residue” and “primer residue”.

Although these are two totally different types of residue-evidence it is often collectively referred to as gunshot residue (GSR). Although GSR is mainly produced by the propellant-powder or the primer, it can also arise from lubricants inside the gun barrel and metals that are found in the bullet or cartridge casing.

Incidentally, the most common chemicals found in primer residue are “lead styphnate”, “antimony sulphide”, and “barium nitrate”. Primer residue will be dealt with in some more detail later in this same posting.

Firearm-related Forensic Phenomenon:
A listing of forensic phenomenon related to firearms and ballistics is endless. However, the most common include bullet holes and bullet damage on various mediums - which obviously also involve gunshot wounds. The reconstruction of bullet trajectories, and the analysis of blood and its associated droplets, splatter and patterns on the scene, are some of the factors that are also scrutinized. As already hinted above, blood found on the scene, and on exhibits such as firearms, can tell a whole story on its own, but let’s keep this posting short, shall we?

In cases where a Forensic Ballistic Specialist was, for whatever reason, not able to be present on the scene while it was still fresh, the specialist will rely on post-mortem reports, as well as photographs and plans of the scene prepared by other police staff. The examination of x-rays, especially with shotgun wounds (Afr: haelgeweer wonde) are sometimes also used to obtain a three-dimensional perspective.

(In South Africa trained staff of the Criminal Record Centre (CRC) are tasked with the responsibility of recording the crime scene and collecting the evidence. Local CRC staff are stationed at centres countrywide. Scenes are recorded by means of photography and sketch plans. Ballistic experts are only called to the scene on the sole discretion of the senior investigating officer in charge. In South Africa there is always at least one Ballistic Expert on standby 24/7 in the main centres of each province where Police Forensic Laboratories are accommodated. These labs are situated in Gauteng, KwaZulu/Natal, Eastern Cape, and Western Cape. Incidentally, the SA Police forensic departments have moved away from using terms such as "expert" or specialist", and prefer using the term "analyst". Yet, when they are called to testify in court their testimony is still referred to as "expert" testimony.)

Sub-fields of Forensic Ballistics:
  • Internal Ballistics
  • External Ballistics
  • Terminal / Wound Ballistics

INTERNAL BALLISTICS: is the study of a projectile's motion from the time the propellant's igniter (the primer) is initiated until the projectile exits the gun barrel. With modern revolvers, for example, the scientific study thus involves the following sequential processes:
  • Applying sufficient pressure on the trigger-lever so that it moves all the way back until it releases the hammer.
  • When the hammer moves forward it impacts the firing pin, which usually floats separately in modern revolvers, which in turn impacts with the cartridge primer, which is a tiny component seated in the rear-end of the cartridge.
  • The primer then sends a small flash, which ignites the propellant contained within the cartridge case.
  • The propellant burns, releasing a large volume of heat and gas within the confines of the cartridge case.
  • The gas pressure forces the bullet, which is seated at the front-end of the cartridge, down the barrel of the gun.
The pressure sensitive ignition compound inside the primer gives off a microscopic vapour-like residue the moment it ignites the propellant powder. Standard police tests for primer residue are usually performed on the hands of a suspect. This residue is NOT gunpowder residue. Gunpowder residue will discharge forward away from the muzzle in tiny particles ranging from burnt, unburnt, and partially burnt propellant powder, as graphically illustrated in the very top picture, and also the video embedded below. Primer residue, on the other hand, will disperse differently in an invisible cloud-like formation leaving traces on the shooter’s hands and also others who happen to be in close proximity of the shooter, but more about this later.

The following very short video shows a bullet leaving a gun barrel filmed at ONE MILLION FRAMES PER SECOND. It was filmed using the Photron SA-1 camera, and clearly shows gunpowder residue being discharged forward out of the muzzle, before and after the bullet has left the barrel:


Sometimes, when the shot is fired at close range these particles can impregnate the skin, leaving small permanent abrasions distributed in a concentric formation, which when still fresh have a reddish brown colour, hence the reason why the phenomenon is often described as “tattooing”, because it CANNOT be washed off. The tattooing-effect can obviously be influenced by other intermediate mediums such as hair or fabric.

The point is – the examination of gunpowder residue patterns, whether it was found on skin or fabric, or both, can greatly assist with the reconstruction of events at the time of the shooting. If the type of firearm and the type of ammunition used is known, then the exact distances between muzzle and target can be determined with reasonable accuracy. In some cases, with the examination of clothing, the distance can be determined with relative accuracy up to a distance of one (1) meter. Bear in mind that these patterns are not always visible to the naked eye, especially when dark coloured fabric is involved, hence the reason why it is preferable to examine such evidence microscopically and also chemically.

Primer Residue:
Primer residue gets deposited on the hands of the shooter the moment the firing-pin impacts the cartridge-primer, in other words, the moment the gun is fired. Trace quantities of the residue will also be deposited on other parts of the shooter that were in close proximity to the gun at the time of discharge. Besides the hand that held the gun, the residue will thus also be deposited on other places such as, arms, neck, face, and also clothing. Although it can be washed off with soap and water, the possibility always exists that not all traces of the invisible residue will be removed. It is thus always better to perform the test as soon as possible, whether or not the suspect shooter has washed hands and arms, or not. The standard procedure is to perform the test a soon as possible on all suspects, including deceased persons. The evidence is usually collected by means of adhesive disks that form part of a collection-kit. Primer residue from a fired gun can be dispersed as far as 1.5 meters and even further, depending on the circumstances. Obviously only a few trace particles of the residue will be present at the farthest point.

The real value of the Primer Residue test is that it can associate an individual with a firearm. It is important, however, to note that this does not identify that person as the shooter. Primer residue can settle on any hand placed near a weapon as it is fired. A person can pick up the residue simply by handling a dirty weapon or discharged ammunition components. - (Sourced from Gunshot Primer Residue – The Invisible Clue)

Linking Fired Bullets to Suspect Firearms:
The most common type of examinations conducted in the category of Internal Ballistics is the identification of fired bullets, cartridge cases or other ammunition components as having been fired from a specific suspect firearm. In other words, it answers questions such as: Were the spent cartridge cases and the fired bullets found on the scene or recovered from the bodies, fired in specific suspect firearm, or not?

The individual characteristics of every firearm are unique (similar to a fingerprint), and are transferred to the bullet and cartridge case during the firing  process. Readers who are interested in the procedures related to Bullet Identification are welcome to visit the website @ www.firearmsid.com.

(A revolver does not eject its spent cartridge cases automatically. They have to be removed manually from the cylinder. With the Griekwastad case I suspect that the fired bullets were not recovered from the scene but were collected during the post-mortem examinations. It is thus safe to assume that these exhibits will have been extensively damaged (depending on the construction of the bullet), and that linking them to the suspect firearm will possibly be a challenge. This aspect then can also be one of the reasons why the investigation is being delayed.)

There are only three (3) conclusions that can be made after microscopically comparing bullet-tests with bullet-evidence:

(Bullet-tests are the “tests” fired in the suspect firearm and are retrieved in an unspoiled state after firing the gun into a custom-designed water tank.)
  • POSITIVE: The bullet was fired from the suspect firearm.
  • NEGATIVE: The bullet was not fired from the suspect firearm.
  • UNDETERMINED: For example: - Due to insufficient marks used for identification purposes it is not possible to conclude whether the suspect-firearm fired bullet’s “x” and “y”.
Bear in mind that if only ONE bullet is linked to the suspect-firearm, then it places that firearm on the scene of the crime... The dilemma, however, is that this type of evidence on its own cannot link a suspect to the actual pulling of the trigger.

An example of a comparison between a test-bullet and a suspect (crime) bullet


EXTERNAL BALLISTICS: deals with the behaviour of the projectile the moment it exits the barrel of the gun and before it hits the target. The calculation and reconstruction of bullet trajectories, and the maximum range of a given bullet, are the two most common types of examinations conducted in this category.

TERMINAL / WOUND BALLISTICS: deals mainly with the study of the projectile’s effect on the target. It can however also deal with the counter-effect of the target on the projectile, in other words, the specific type of damage on the bullet caused by a specific target, whether it be wood, glass, metal, flesh, or bone. When the target is biological tissue, it is common practice to use the term “Wound Ballistics”.

Terminal / Wound Ballistics is a multifaceted field on its own, which can take many years of study, practical experience, and extensive research to master. Incidentally, one of the world’s leading experts in this field is Dr. Vincent J. M. Di Maio, an American pathologist and author of Gunshot Wounds: Practical Aspects of Firearms, Ballistics, and Forensic Techniques (1992) (2e: 1999) ISBN: 978-0849381638.

The most common types of examinations conducted in this category are:
  • The determination of the distance between firing point and target (as already briefly discussed above).
  • Establishing whether a particular wound was caused by a fired bullet, or not.
  • Determining the calibre and type of projectile that caused bullet damage or gunshot wound.
  • Identifying the bullet exit and entrance by examining the holes in targets, or the wounds in biological tissue.
  • The examination of ricochet possibilities on targets and fired projectiles.
Wound Ballistics is often subdivided into the following separate categories, for example:
  • Hard-contact and loose-contact gunshot wounds.
  • Near contact gunshot wounds.
  • Intermediate gunshot wounds.
  • Distant gunshot wounds.
In contact wounds the muzzle of the firearm is held against the surface of the body at the time of discharge. In hard-contact wounds, the muzzle is jammed "hard" against the body, causing the edges of the entrance wound to be seared by the hot gases of combustion and blackened by the soot, which is embedded in the seared skin and cannot be removed. (Source: Di Maio - Gunshot Wounds 2nd Edition - Pg.65)

The Trace Metal Detection Test (TMDT)
In my initial posting concerning the Griekwastad tragedy I made mention of the “trace metal detection test”. This was a test that we often used at crimes scenes to determine whether a person’s hands had actually been in contact with a metal object, for example, a firearm. A few minutes of exposure to the metal parts of a revolver, for example, will leave detectable residue on a person’s hands. The location, size, and shape of the traces on the hand and fingers will form patterns consistent with the location, size, and shape of metal parts on the revolver, for example the trigger. In fact I’ve often seen the test producing excellent results on the trigger-finger that reveal the exact same impression and pattern of the trigger of the suspect firearm. I’m not sure, however, if this test is still being used by the SA Police, or not. For more info and references see the Wikipedia Page dealing with The Trace Metal Detection Test (TMDT).

A final word on criminal intent (doli capax) of a juvenile:
Taken from a quotation from Russell on Crime, 10th ed. vol.I at p 43 at p 356:
The modern rule is that a child of eight and under fourteen is presumed to be incapable of criminal intent (doli capax): but the presumption may be rebutted and weakens with the advance of the child’s years towards fourteen, and the particular facts and circumstances attending the doing of the act and manifesting the understanding of the child. The evidence of mens rea which is allowed to displace the presumption (expressed in the ancient phrase malitia supplet aetatem) should be strong and clear beyond reasonable doubt.

*******************************************

This concludes the series of updates concerning this case. This blog will not be delivering any further updates until an arrest or final conclusions have been made.

Readers are welcome to leave comments and ask questions, but bear in mind that I will not be answering any questions pertaining to the guilt or non-guilt of anybody until an official verdict has been pronounced.

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