Forensic Science Techniques
Forensic Science Techniques of Forensic Science
Introduction to Forensic Science Techniques
Forensic science uses sophisticated laboratory techniques to detect the presence of substances in the victim, in the suspected criminal, or at the crime scene. For example, in determining whether alcohol was involved in a crime, the amount of alcohol in the blood can be measured in two ways. One is to measure the amount of alcohol exhaled in the breath of an individual, which reveals the concentration of alcohol in the person’s blood. Recent advances in technology have produced alcohol breath-testing instruments so accurate that their results are evidential (capable of providing evidence in court). Blood-alcohol level can also be determined by actual blood tests, usually through gas chromatography. In this method, the blood sample is vaporized by high temperature, and the gas is then sent through a column that separates the various chemical compounds present in the blood. Gas chromatography permits the detection not only of alcohol but also of other drugs, such as barbiturates, cocaine, amphetamines, and heroin.
When a body is discovered in a lake, stream, river, or ocean and the lungs are found to be filled with water, the medical examiner must determine if the drowning occurred where the body was found or elsewhere. A standard microscope that can magnify objects to 1500 times their actual size is used to look for the presence or absence of diatoms, single-celled algae that are found in all natural bodies of water. The absence of diatoms raises the possibility that the drowning took place in a sink or bathtub, not where the body was found, since diatoms are filtered from household water during treatment.
A scanning electron microscope that can magnify objects 100,000 times is used to detect the minute gunpowder particles present on the hand of a person who has recently fired a gun. These particles can also be chemically analyzed to identify their origin from a particular type of bullet.
Forensic examination of substances found at a crime scene can often establish the presence of the suspect at the scene. One of the oldest techniques of forensic science is dusting the scene of a crime for fingerprints, impressions of the fingertips left on surfaces touched bare-handed. In one method of obtaining a fingerprint, a technician spreads fine powder over a surface with a brush or magnetic wand. The powder sticks to proteins secreted by the sweat glands on the skin ridges of the fingertips. When the excess powder is removed, an outline of the contours of the ridges remains. In other methods, the print may be chemically treated to reveal the contours. Because no two fingerprints are the same, fingerprinting provides a positive means of identification. Computer technology now allows law-enforcement officers to record fingerprints digitally and to transmit and receive fingerprint information electronically (see Electronics) for rapid identification.
Other evidence present at a crime scene may include blood, hair, skin, or semen. Recent developments in technology now allow scientists to examine the deoxyribonucleic acid (DNA), or genetic material, of these substances to establish whether they belong to the victim or to a suspected assailant. By means of a high-technology method known as the polymerase chain reaction (PCR), a laboratory can rapidly clone, or multiply, the DNA from a tiny sample of any of these substances. This process produces enough DNA to compare with a sample of DNA taken from a suspected criminal. The use of DNA for such identification purposes is commonly referred to as DNA fingerprinting.
Human bite marks can also serve as circumstantial evidence. Such bites may be found upon the body of a homicide victim or within pieces of food or other objects, such as chewing gum, found at the crime scene. A forensic scientist can fill the impressions caused by these bites with liquid plastic. Upon hardening, the cast formed is an extremely accurate replica of the assailant’s teeth, which can be compared with a cast made from the teeth of the suspect.” (1)
Digital Forensics Investigation
Digital Devices and their associated applications and operating systems contain huge quantities of data which can play a critical role within an investigation. Correctly extracting and presenting this data requires both specialist skills and equipment and furthermore can only be relied upon in a court if the material has been acquired and analysed in a evidentially robust manner by a trained individual.
There are a number of individuals who have a requirement or desire to be able to forensically retrieve data from mobile phones, computers and other digital storage devices. They can apply an investigative mindset to interrogating multiple complex data sets, understanding their content, its implications on an investigation and then how to present your findings in an evidentially acceptable, intelligent manner.
Digital device examiners have exposure to the multiple forensic tools available and insights into current and upcoming legislative procedures and best practice.
This section covers the appropriate legislative considerations when practicing Digital Forensics.
Complex Digital Investigation
It is widely accepted that all investigations from the complex, high profile cased to the smaller volume crime will now have some form of digital footprint. Often, intelligent use of digital investigation techniques can be the difference between a positive or negative result in locating & apprehending a suspect or into the criminal justice process in a court of law.
Law enforcement officers should consider and balance the opportunities and benefits against the restrictions and risks associated with each discipline of digital investigation and how they can operate and compliment when intelligently cross referenced as part of an investigation strategy.
Communications Data Investigation
Communications Data is an essential tool for law enforcement that has been utilised in intelligence and in evidence for many years. Many high profile, complex cases have had a breakthrough as a result of the acquisition and subsequent analysis and evidential package of communications data in a court of law. When presented effectively alongside other evidence, communications data is a powerful component of a prosecution case which is often seen as the glue which ties the accused to the events.
There are key differences and opportunities afforded by traditional telephony, SMS & GPRS data against current and emerging data sets including VOIP, WiFi Calling, Packet Data as communication platforms continue to evolve.
Notes and References
- Information about Forensic Science Techniques in the Encarta Online Encyclopedia