Criminalistics (or Criminal Forensics)
Criminalistics involves the proper, forensically-sound gathering, preservation and examination of physical evidence - usually related to a crime. Although we do not employ crime scene technicians, our detectives possess extensive police training and experience, particular in crime scene investigation and the handling of evidence, and they are amply qualified to gather, handle, catalogue and present physical evidence in a manner that will preserve the integrity of that evidence; and we are able to have that evidence examined and analyzed by leading technologists and laboratory scientists who are able make determinations and present expert testimony that will carry weight in both criminal and civil court.
What evidence can be collected and analyzed?
Although this is not intended to be an exhaustive list, criminalistics deals commonly with the following types of evidence:
Fingerprints, Palmprints and Toeprints
Dactyloscopy or fingerprint identification is the scientific process of examining and comparing the characteristics of two instances of fingerprints, palmprints or toeprints to determine whether they could have come from the same individual. Fingerprints left at a crime scene, for example, might be compared with fingerprints on record for known offenders within the area with a similar modus operandi. Fingerprints that have been obtained from a person directly, such as at the time of a person's arrest or when applying for a passport, are called exemplar, control or known prints. Prints found at a crime scene or through other methods will usually not be of the same quality as an exemplar as they're quite often smudged, overlapping or only provide a small portion of the fingerprint. Prints can be left on various surfaces for different reasons, and can be classified accordingly as:
- Latent Prints - these are usually invisible or difficult to see with the naked eye, that are caused by contact between the ridges of the skin and a surface. Any residue on the skin, like sweat, oil, grease, blood can be deposited onto that surface and will create an impression resembling the person's fingerprint. Electronic, chemical and physical processing techniques can be used to visualize and "lift" latent prints from almost any type of surface.
- Patent Prints - these are visible to the naked eye and do not require enhancement as in the case of latent prints. Patent prints are usually photographed instead of being "lifted". These types of prints are caused by the transfer of foreign matter from the finger, palm or foot onto a surface. The foreign matter could be dry as in the case of flour or dirt, or fluid like blood or paint.
- Plastic Prints - these are impressions left in a material or substance that retains the shape of the ridge detail. Examples of such materials might be melted candle wax, putty from a window, wet paint or thick grease.
- Digital Prints - these are impressions that have been captured by a digital recording device such as a scanner, camera or other technology (usually by accident) that can be identified and easily examined for similarities with a known print.
- Outsole impressions - these are impressions left on an object or surface and that was caused by direct contact between that object or surface and the exterior of the footwear. Outsole impressions can be left on the ground from walking, on doors or walls from kicking or climbling and on the bodies of people or animals that have been kicked, stomped or jumped on.
- Latent impressions - in addition to visible indentations on surfaces left by forceful contact, latent impressions can also be deposited on surfaces that might apear invisible to the naked eye. Recovering these types of impressions can usually be done with gel or electrostatic dust lifters after latent prints have been identified using specialized light sources
- Insole imprints - these are imprints left by the person's foot on the interior of footwear. It requires the footwear to be Analysis of the insole imprints can be used to link a person(s) to a piece of footwear.
- Footwear trace evidence - Footwear trace evidence is trace evidence that is recovered from footwear. Types of trace evidence that could be recovered include skin, glass fragments, body hair, fibers from clothing or carpets, soil particles, dust and bodily fluids. The study of this trace evidence could be used to link a piece of footwear to a location or owner. DNA can be one of the contributing factors in forensic footwear evidence.
The field of tool mark examination is very closely linked to forensic work involving firearms and ammunition which also deals with impressions and marks left on cartridges and projectiles by the weapon's firing pin or barreling. Tool mark examination seeks to identify the type of tool, weapon or instrument that was used in the commission of a crime by matching the marks left by the tool at the scene of the crime with exemplars made under controlled laboratory conditions as well as examining any material transferred between the tool and the scene (including microscopic, metallurgic, and chemical composition analysis). The two main types of marks are impressed marks, such as a hammer strike, and striated marks, such like those created by a screwdriver scraping the surface of a softer object. These can be even further categorized as:
- Impressed marks, e.g. Hammer Marks
- Mainly impressed marks, e.g. Levering marks, Impact marks and Gripping marks
- Striated marks, e.g. Sliding marks, Double-blade cutting marks and Stab marks
- Dynamic marks, e.g. Levering marks with Striations and Saw marks
- Specialized marks, e.g. Punch marks, Drill marks and Slide hammer marks
Windows, mirrors, bottles and other glass objects can be vital evidence in housebreaking, assault, murder, hit-and-run and other crimes. A person run over by a vehicle may break a headlight or lamp in the impact, possibly even the windshield, and tiny fragments of glass would be found on the victim's clothing and person that could be connected to the vehicle. In fact, when any sort of glass is broken minute fragments will be propelled some distance and any persons in close proximity to that object will pick up fragments, even microscopic fragments, which can ultimately be matched to the object that was broken. Apart from associating two fragments of glass with one another, glass fragment examination can also be used to determine the following sorts of things:
- If a window was struck with a blunt instrument like a brick or bat, it is possible to determine which side was struck and the degree of the force used
- If a window has been penetrated by a bullet or other projectile or missile, it is possible to determine the direction from which it was fired.
- If two or more bullet holes are in close proximity, it is possible to determine the sequence of firing.
Hairs and Fibers
Many crimes involve direct physical contact between the perpetrator and the victim, and where such contact takes place it is almost a certainty that microscopic evidence will be transferred between them. Hairs and fibers are easily transferred in this manner and are commonly found at crime scenes and on suspect's clothing and belongings. An analysis of hairs and fibers can provide the following information for investigators and prosecutors:
- Fibers can be classified as being of animal, vegetable, mineral or synthetic composition and even a fiber's sub-classification can be determined, e.g. polyester, cotton, nylon etc.
- It can be determined whether questioned fibers are the same type and color as the standard or exemplar.
- It can be determined whether questioned and exemplar fibers share microscopic characteristics, and whether they are common or rare
- An scientific opinion can be made as to whether questioned fibers could have originated from the same source as the exemplar.
- Hairs can be identified as human or animal and even which race or species they originate from.
- The area of the body the hair originated can be deduced as well as how the hair was removed (e.g. by force or naturally)
- Hair can be analyzed to determine whether it has been treated, cut, bleached or dyed
- Whether a questioned hair could have originated from the same source as the exemplar (using macroscopic and microscopic comparison).
Other Types of Evidence
In addition to the above, the following types of evidence are also of vital importance to criminal investigators, and would be collected, preserved, processed and analyzed if present at a crime scene. If you're interested in learning more about these last few items then keep a look out for an upcoming article currently being written by a forensic scientist from the South African Police Service's Forensic Science Laboratory or subscribe to our newsletter to receive a copy before it is published on our blog.
- Blood patterns, stains and spatter
- Tyre tracks and skid marks
- Paint chips and paint transfer
- Trace evidence
- Biological evidence, including semen, saliva and perspiration
- Ballistics (Internal, External, Transitional and Terminal)
- Soil and organic matter
- Fire residues and debris
- Drugs and controlled substances