| Terminology of Firearms |
[10 Jun 2003|02:18am] |
Action : The part of a firearm that loads, fires, and ejects a cartridge. Includes lever action, pump action, bolt action, and semi-automatic. The first three are found in weapons that fire a single shot. Firearms that can shoot multiple rounds [repeaters] include all these types of actions, but only the semi-automatic does not require manual operation between rounds. A truly automatic action is found on a machine gun.
Barrel : The metal tube through which the bullet is fired.
Black Powder : The old form of gunpowder invented over a thousand years ago and consisting of nitrate, charcoal, and sulfur.
Bore : The inside of the barrel. Smoothbore weapons [typically shotguns] have no rifling. Most handguns and rifles have "rifling".
Breech : The end of the barrel attached to the action.
Bullets : The projectile. They are shaped or composed differently for a variety of purposes :
Round-nose - The end of the bullet is blunted.
Hollow-point - There is a hole in the bullet that creates expansion when a target is struck, creating more damage.
Jacketed - The soft lead is surrounded by another metal, usually copper, that allows the bullet to penetrate a target more easily.
Wadcutter - The front of the bullet is flattened.
Semi-wadcutter - Intermediate between round-nose and wadcutter.
Semi-wadcutter - Features of both semi-wadcutter and hollowpoint.
Butt or buttstock : The portion of the gun which is held or shouldered.
Calibre : The diameter of the bore measured from land to land, usually expressed in hundredths of an inch [.22 cal] or in millimeters [9mm].
Cartridge : Also called a round. Made up of a case, primer, powder, and bullet.
Centerfire: The cartridge contains the primer in the center of the base, where it can be struck by the firing pin of the action.
Chamber : The portion of the action that holds the cartridge ready for firing.
Choke : A constriction of a shotgun bore at the muzzle that determines the pattern of the fired shot.
Double-action : Pulling the trigger both cocks the hammer and fires the gun.
Double barrel : Two barrels side by side or one on top of the other, usually on a shotgun.
Gauge : Refers to the diameter of the barrel on a shotgun in terms of the number of lead balls the size of the bore it would take to weigh one pound [10 gauge, 12 gauge, etc] ".410 gauge" actually refers to calibre, but is worded as such to refer to a shotgun.
Hammer : A metal rod or plate that strikes the cartridge primer to detonate the powder.
Ignition : The way in which powder is ignited. Old muzzle-loading weapons used flintlock or percussion caps. Modern guns use primers that are rimfire or centerfire.
Lands and grooves : Lands are the metal inside the barrel left after the spiral grooves are cut to produce the rifling.
Magazine : This is a device for storing cartridges in a repeating firearm for loading into the chamber. Also referred to as a clip.
Magnum : An improved version of a standard cartridge which uses the same caliber and bullet but has more powder, giving the fired bullet more energy. Magnum shotgun loads, however, refer to an increased amount of shot pellets in the shell.
Muzzle : The end of the barrel out of which the bullet exits.
Pistol : Synonym for a handgun that does not have a revolving cylinder.
Powder : Modern gun cartridges use smokeless powder that is relatively stable, of uniform quality, and leaves little residue when ignited. For centuries, black powder was used and was quite volatile [ignited at low temperature or shock], was composed of irregularly sized grains and left a heavy residue after ignition, requiring frequent cleaning of bore.
Primer : A volatile substance that ignites when struck to detonate the powder in a cartridge. Rimfire cartridges have primer inside the base, while centerfire cartridges have primer in a hole in the middle of the base of the cartridge case.
Revolver : Handgun that has a cylinder with holes to contain the cartridges. The cylinder revolves to bring the cartridge into position to be fired. This is single-action when the hammer must be cocked before the trigger can fire the weapon. It is "double-action" when pulling the trigger both cocks and fires the gun.
Rifling : The spiral grooves cut inside a gun barrel that give the bullet a spinning motion. The metal between the grooves is called a land.
Rimfire : The cartridge has the primer distributed around the periphery of the base.
Safety : A mechanism on an action to prevent firing of the gun.
Shotgun : A gun with a smoothbore that shoots cartridges that contain shot or small metal pellets [of lead or steel] as the projectiles.
Sights : The device[s] on top of a barrel that allow the gun to be aimed.
Silencer : A device that fits over the muzzle of the barrel to muffle the sound of a gunshot. Most work by baffling the escape of gases.
Single-action : The hammer must be manually cocked before the trigger can be pulled to fire the gun.
Smokeless powder : Refers to modern gunpowder, which is really not powder but flakes of nitrocellulose and other substances. Not really smokeless, but significantly less than black powder.
Stock : A wood, metal, or plastic frame that holds the barrel and action and allows the gun to be held firmly.
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| Crime Scene Investigation |
[17 May 2003|03:20pm] |
Definition : Reconstruction
The use of scientific methods, physical evidence, deductive reasoning and their inter-relationships to gain explicit knowledge of the series of events that surround the commission of a crime.
Types of Reconstruction
1 : Specific Incident Reconstruction [traffic accident, homicide, bombing, etc.]
2 : Specific Event Reconstruction [sequence, direction, condition, relation, identity]
3 : Specific Physical Evidence Reconstruction [firearms, blood, glass, etc.]
In any given scene it may be possible to do a total or only partial reconstruction, and the reconstruction may use more than one technique [i.e. both trajectory and blood stain pattern reconstruction to locate the position of the victim]. Some scenes lend themselves to reconstruction better than others. Traffic accidents are common scenes to reconstruct and often can be thoroughly reconstructed. Vehicles are rather massive objects that obey the laws of motion and often leave a wealth of physical evidence behind before, during and after an accident. It may be possible to show the entire sequence of events from the time the vehicles first enter the area of the accident until they come to rest following the accident.
Scenes involving the movement of people are more difficult. While it may be possible to say where a person was at the scene at several points in time, the manner in which they moved in the scene cannot be reconstructed. People may move slowly, quickly, hesitantly, jump up and down, run, skip, fall down, etc; all without leaving any particular trace behind. That said, there are, of course, the odd cases where the amount and type of physical evidence does allow the paths of the participants to be tracked with some accuracy; however, the vagaries of facial expression, gestures, and body language are simply impossible to reconstruct at all.
Below are some examples of the types of information which reconstruction may provide. Some items also appear in more than one category, and it may be possible to use information from several areas to complete or validate the final reconstruction.
Examples of Types of Reconstruction
Physical
1 : Blood and Blood Stain Pattern Analysis
2 : Identity of victim/offender
3 : Position and location of the victim
4 : Position and location of the offender
5 : Movement by the victim/offender at the scene
6 : May identify the location of the scene [if the victim is removed and left elsewhere]
7 : May indicate a staged or secondary scene
8 : Minimum number of blows struck
9 : Type of weapon used
Documents
1 : Reassembly of torn or shredded papers
2 : Recovery of obliterated writing
3 : Comparison of handwriting
Firearms
1 : Trajectory
2 : Shooting distance
3 : Position and location of the victim
4 : Position and location of the offender
5 : Sequence of shot/s
6 : Direction of shot/s
7 : Possibility that the wound/s could have been self-inflicted
8 : Identification of weapon used may link serial cases
Functional Evidence
1 : Does the weapon or vehicle function properly?
2 : Semi-automatic with slide locked back may indicate last round was fired
3 : TV or coffee pot on at scene
4 : Do door/window locks properly secure?
Glass
1 : Direction of break [from which side of the glass]
2 : Sequence of shots [it should be noted that current research indicates that sequencing of shots through laminated automotive glass is not reliable]
Impression Evidence : Fingerprints, shoe prints, tire tracks
1 : Identity of victim/offender
1 : Place victim/offender at the scene and at specific sites at the scene
1 : Fingerprints may indicate where the offender/victim was at the scene or how an object was held
1 : Shoe prints may show location and movement through the scene
1 : Tire tracks may show vehicle position and direction of travel and may indicate the type of vehicle driven
Ligature
1 : Type of ligature used [if missing]
2 : Use of same/similar ligature can be used to link serial cases
3 : Type of ligature used may indicate offender's occupation or interests [i.e. rope tied with knots commonly used by dock workers or climbers]
Pathology
1 : Manner of death [homicide, suicide, natural, accidental]
1 : Time of death [approximate]
1 : Cause of death
1 : Time before incapacitation from wounds [approximate]
1 : Whether injuries were sustained pre or post-mortem
1 : Identity and/or age of victim
1 : Signs and manner of sexual assault [if any]
1 : Possibility that the wound/s could have been self-inflicted
Physical Match : Reassembly of broken objects
1 : Bombs
1 : Vehicle lamps, mirrors and windows
1 : Aircraft which may have crashed and/or exploded
Relational/Positional Evidence
1 : Blood drops on the threshold of a door indicate that the door was open when the blood was shed
2 : Location of other objects and their condition may also indicate a variety of contributing factors depending on the specifics of the crime
Trace Evidence
1 : Trajectory of projectiles based on retention of material through which they have passed
2 : Place offender/victim at the scene, and at specific sites at the scene
3 : Describes the environment of an unknown crime scene
4 : May indicate offender occupation
5 : Vehicle positions, speeds, sequence of accident events
Information Needed For Reconstruction
Information may come from physical evidence, witness statements, and the reports of experts. The reconstructionist examines all scene photographs, autopsy protocol and photographs, measurements, drawings, notes, reports and items of evidence. Complete and accurate documentation of the scene is essential. Depending on the type of reconstruction being done this may include some different things, such as the height and vertical/horizontal angles of shots into a wall, or the length and width of a bloodstain.
Steps in Reconstruction
1 : Recognition of evidence
2 : Documentation of evidence
3 : Collection of evidence
4 : Evaluation of evidence
5 : Hypothesis of evidence
6 : Testing of evidence
1 : Reconstruction of evidence
Step 1 : Recognition of evidence is arguably the most important. Unless the potential evidence can be recognised, no further reconstruction can be carried out.
Steps 1 - 3 : Recognition, Documentation and Collection of evidence are the heart of any successful scene investigation, and form the basis for the reconstruction.
Step 4 : Evaluation of evidence examines the evidence [possibly following laboratory analysis] and looks at what information the evidence provides and how reliable it is. At this time any witness statements should be compared to the evidence to see which parts of the statements can be supported or refuted by the evidence.
Step 5 : Hypothesis is the formulation of an idea of how the event [or portions of it] occurred. This is not merely conjecture and should be firmly supported by the evidence.
Step 6 : Testing looks to see how the hypothesis developed in Step 5 can be validated. This is accomplished by comparing the evidence against known physical laws or devising a test to attempt to replicate the event [or the relevant segment].
Step 7 : Reconstruction is the reporting of the results of the analysis. The results are reported as a range, where the event [or portions of it]:
A. Can be shown to have occurred in a given manner
B. Can be shown to be likely to have occurred in a given manner
C. Can be shown to be unlikely to have occurred in a given manner
D. Can be shown not to have occurred in a given manner</b>
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| Fingerprints |
[22 Jan 2003|07:22pm] |
A fingerprint is an impression of the friction ridges found on the inner surface of a finger or a thumb. The science of fingerprinting constitutes the only unchangeable and infallible means of positive identification known to man. The reasons why fingerprints are used for identification purposes are outlined below. These premises are supported by scientific research in areas such as biology, embryology, anatomy and histology, to name a few.
1. Ridge patterns and the details in small areas of friction ridges are unique and never repeated
2. Friction ridges develop on the fetus in their definitive form before birth
3. Ridges are persistent throughout life except for permanent scarring
4. Friction ridge patterns vary within limits which allow for classification
The fourth premise is not really a fact relating to identification. Fingerprint classification assists to narrow the search but is not part of the actual identification process. Its importance is clear, though, if you consider the huge task you would be faced with if, after taking thousands and thousands of fingerprints, you had no method to file and retrieve them.
In order to gain a more in-depth understanding of the principles of fingerprint identification, the identification specialist needs to have knowledge of the actual biological structure of friction skin and understand the stages of friction skin development on the foetus prior to birth and, the numerous factors that affect its growth.
Identical twins have the same DNA configuration but they do not have identical friction ridge configuration.
( +definitions+ )
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| Luminol |
[06 Dec 2002|05:18pm] |
Much of crime scene investigation is based on the notion that nothing vanishes without a trace. This is particularly true of violent crime victims. A murderer can dispose of the victim's body and mop up the pools of blood, but without some heavy-duty cleaning chemicals, some evidence will remain. Tiny particles of blood will cling to most surfaces for many years, without anyone ever knowing it is there.
The basic idea of luminol is to reveal these traces with a light-producing chemical reaction between several chemicals and haemoglobin, an oxygen-carrying protein in the blood. The molecules break down and the atoms rearrange to form different molecules. In this particular reaction, the reactants [original molecules] have more energy than the products [resulting molecules]. The molecules get rid of the extra energy in the form of visible light photons. This process, generally known as chemiluminescence, is the same phenomenon that makes fireflies and light sticks glow.
Before spraying luminol, there is no sign of blood. After spraying luminol, the latent blood traces emit a blue glow. Investigators will spray a suspicious area, turn out all the lights and block the windows, and look for a bluish-green light. If there are any blood traces in the area, they will glow.
The central chemical in this reaction is luminol [C8H7O3N3], a powdery compound made up of nitrogen, hydrogen, oxygen and carbon. Criminalists mix the luminol powder with a liquid containing hydrogen peroxide [H2O2], a hydroxide [OH-] and other chemicals, and pour the liquid into a spray bottle. The hydrogen peroxide and the luminol are actually the principle players in the chemical reaction, but in order to produce a strong glow, they need a catalyst to accelerate the process. The mixture is actually detecting the presence of such a catalyst, in this case the iron in haemoglobin.
To perform a luminol test, the criminalists simply spray the mixture wherever they think blood might be. If haemoglobin and the luminol mixture come in contact, the iron in the haemoglobin accelerates a reaction between the hydrogen peroxide and the luminol. In this oxidation reaction, the luminol loses nitrogen and hydrogen atoms and gains oxygen atoms, resulting in a compound called 3-aminophthalate. The reaction leaves the 3-aminophthalate in an energized state -- the electrons in the oxygen atoms are boosted to higher orbitals. The electrons quickly fall back to a lower energy level, emitting the extra energy as a light photon. With iron accelerating the process, the light is bright enough to see in a dark room.
The before and after effects of luminol.
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| Soil and Mud |
[06 Dec 2002|12:01pm] |
An important, but elusive source of information, can be the earth around the crime scene. Having taken soil samples during the search for other evidence, investigators can use precise techniques to check corresponding traces of soil or mud on a suspect's clothes, or the tires or bodywork of a suspect vehicle.
Conversely, if a person is arrested on suspicion of having committed a crime, but the scene of that crime has not yet been established, traces of soil found on the suspect, or in their living quarters or vehicle, for example, can suggest a particular locality, when unusual soil constituents or vegetation are involved.
One of the most common techniques used to compare soil samples involves a density-gradient tube. It is a long, narrow, glass tube that is filled with mixtures of two chemicals of different density. The mixtures have differing proportions of the two chemicals, and are arranged in the tube so that the mixture with the greatest proportion of the heavier chemical provides the bottom layer. Succeeding layers contain progressively smaller proportions of the heavier chemical, so that the top layer, with the smallest proportion of the heavier chemical, is the least dense.
When a sample of soil is poured into the density-gradient tube, each particle sinks until it reaches a layer that is of a density equal to its own, where it remains suspended in the liquid. Each soil sample consists of particles of different densities, which reveal themselves as dark bands of suspended particles in the tube's different layers. If a second tube is made up of identical density bands of liquid, and a second soil sample is poured into it in the same way, examiners can see whether or not the bands of particles match.
They often take samples at intervals to as far as one hundred yards from the actual crime scene, for purposes of comparison. The evaluation of samples in this way can also be useful in checking a suspect's alibi, or putting the suspect directly at the scene of the crime.
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| Mortis |
[04 Dec 2002|01:25am] |
Medical experts can estimate the time of death, and sometimes glean other clues from the phenomena of postmortem lividity and rigor mortis. Postmortem lividity, also called livor mortis, is a purplish 'liver' discolouration on the part of the body facing the ground [the part of the body facing up appears pale].
Caused by the pooling of blood within blood vessels from the effect of gravity, lividity begins about thirty minutes after death.. If, in the early stages of lividity, one presses a finger firmly against the discoloured skin, the pressure will cause 'blanching'. When pressure is released, the discolouration returns. Four or five hours after death, however, the discolouration becomes clotted and pressure will no longer cause blanching.
A related phenomenon, fixed lividity, can also provide important clues. Lividity becomes 'fixed' in eight to ten hours, meaning that if the body has remained in the same position for that period of time, the livor mortis can no longer be significantly shifted by changing the position of the body. Consequently, if lividity is observed on the back of a body found lying face down, investigators can be sure that the body was turned over after death and possibly moved from another site.
Immediately following death, the muscles relax and then become rigid without the shortening of muscle. Rigor mortis, the stiffening of a body, manifests itself within the first two to four hours. Stiffening is first noticeable in very small muscles, including the eyelids, face, and lower jaw. It then spreads to the neck and the rest of the body.
After rigor mortis has spread throughout the entire body, it begins to disappear in the same order that it first became noticeable - small muscles first, followed by large muscles. After about forty-eight to sixty hours, all the muscles are again relaxed. This is due to the decomposition of the muscle fibres.
While short term postmortem changes follow a fairly predictable course, they are affected by such factors as where the body is found - water, buried in soil, or the the desert, for example. In addition, numerous environmental factors can affect the rate at which decomposition occurs over longer periods, and complicate efforts to determine when a person died.
Temperature and humidity are two key variables. Low temperatures and low humidity slow decomposition; high temperatures and humidity accelerate it. On the other hand, in a moist, tropical climate, a corpse left outside can become skeletonised in a few weeks. In part, this is because such a climate is ideal for insects that feed on decomposing flesh.
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| Forensic Entomology |
[04 Dec 2002|01:24am] |
.. is the study of insects associated with death, and can be a valuable tool in homicide investigations. Because the scent of a corpse attracts insects and triggers predictable insect activity, and because the life cycles of the various insects on the body are fixed and precise, forensic entomologists can work backwards to accurately estimate time of death. Bug behaviour can also indicated whether the victim was killed indoors or outdoors, during the day or night, in warm or cold weather, and in shade or in sunlight.
TIMELINE OF INSECT ACTIVITY
10 minutes : Ten minutes after the body is dead in open air, flies arrive and lay thousands of eggs in the mouth, nose, and eyes of the corpse.
12 hours : Eggs hatch and maggots feed on tissues.
24 - 38 hours : Beetles arrive and feast on dry skin.
48 hours : Spiders, mites, and millipedes arrive to feed on the bugs which are already there.
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| Glass |
[04 Dec 2002|01:23am] |
When a piece of glass shatters into countless fragments, all of those fragments have identical properties. The colour, density, dispersion, and refractive index [the way light is bent when it travels through a substance other than air], will all be the same.
When bullets are fired through glass, three things can be determined :
1 : Which side the shooter fired from
2 : The angle from which the shot was fired
3 : The sequence in which multiple shots were fired
Intuitively, we would think that when someone shoots through glass, the broken pieces will be found on the opposite side. That is not the case, however. When glass breaks from applied force, it spins back toward the force; not away from it. This is because glass is elastic, therefore it bends, and snaps back violently; creating blowback. In fact, blowback can throw particles as far as eighteen feet in the direction from which the projectile originated.
From this, investigators can determine the distance of where the shooter was standing, by checking particles found on the ground. In addition, it is possible to determine where a shot came from by looking at the type of angled hole the bullet left in the glass. A sheet of glass also outlines the order in which shots were fired through it.
Albeit shattering glass is a staple of normality, tempered glass [glass held secure by a frame] will usually crack before it shatters. Several bullets are required to shatter a pane of glass, and under certain circumstances the pattern of cracks can indicate the sequence of shots.
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| Graphology |
[04 Dec 2002|01:22am] |
There are seven different units responsible for investigating anything in relation to paper.
1 : Machines used to create documents
2 : Paper
3 : Ink
4 : Manufacturer/s
5 : Subsequent microscopic findings [ie, hair, fibres, fingerprints]
6 : Meanings of words and/or numbers
7 : Breaking of codes
The basic philosophy behind document examination, or questioned document examination, is similar to that of other forms of physical evidence and evaluation. Scientists and investigators look for characteristics that vary from one sample to another. Signature and handwriting constitute unique characteristics. Just as no two people share the same identical fingerprints, no two people write exactly the same way. Handwriting comparison is the most common type of document examination because forgery and fraud are as old as writing itself.
Distinction must be made between handwriting identification and handwriting analysis, or graphology. The former, which is carried out by forensic linguists, concentrates on the many factors that make up what is called 'brain writing' [writing which a person does habitually, without thinking about it], including the unconscious movements that make each person's writing unique and identifiable.
There is no standard procedure for making a handwriting comparison. Graphologists use elements in the writing, including slant, zone, upper and lower loop formations, and any number of other repeated details which help to signal specific, potential behavioral features about the writer.
Everything about paper and writing can be tested. Writing instruments, such as pens, pencils, quills, paintbrushes, etc, can be checked for class characteristics using visual inspection and stereomicroscopic examination. Occasionally, striation marks may appear in ballpoint pen writing, and become an individual characteristic reflecting wear and tear on the instrument.
Paper can be tested for its chemical makeup, color, size, shape, weight, watermarks, surface texture and appearance, flurorescence, and any other properties aiding in identification. The dye used in coloured papers can be identified by a technique called thin layer chromatography. Other methods of chemistry can detect trace elements added to paper and can distinguish a paper's specialised fillers.
The pigment in ink remains on the surface of the paper but the solvent used to carry the pigment is absorbed into the fibres. While the pigment can be removed, the solvent will remain. Examiners can often makie it visible by using different types of light and filters.
Other techniques such as the use of an electrostastic detection apparatus can enable examiners to pick up the impression of what was written on the paper underneath the original document. A substance called parylene can give strength and resiliency to extremely brittle or crumpled material, allowing it to be opened, smoothed, and read.
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