Thursday, November 23, 2006


Forensic science
Forensic science (often shortened to forensics) is the application of a broad spectrum of sciences to answer questions of interest to the legal system. This may be in relation to a crime or to a civil action. The use of the term "forensics" in place of "forensic science" could be considered incorrect; the term "forensic" is effectively a synonym for "legal" or "related to courts" (from Latin, it means "before the forum"). However, it is now so closely associated with the scientific field that many dictionaries include the meaning given here.
Criminalistics is the application of various sciences to answer questions relating to examination and comparison of biological evidence, trace evidence, impression evidence (such as fingerprints, shoeprints, and tire tracks), controlled substances, firearms, and other evidence in criminal investigations. Some of the forensic science disciplines are:
Forensic odontology is the study of the uniqueness of dentition.
Forensic toxicology is the study of the effect of drugs and poisons on the human body.
Forensic engineering studies the causes of failure of devices and structures.
Forensic accounting is the study and interpretation of accounting evidence.
Forensic psychology and forensic psychiatry deal with the legal aspects of human behavior.
Forensic anthropology is the application of physical anthropology in a legal setting, usually for the recovery and identification of skeletonized human remains.
Forensic entomology deals with the examination of insects in, on, and around human remains to assist in determination of time or location of death.
Forensic evidence deals with scientific evidence from a crime scene to convict a possible criminal.
Questioned document examination is the study and interpretation of evidence that takes the form of document.
Forensic history
The "Eureka" legend of Archimedes (287-212 BC) can be considered an early account of the use of forensic science. In this case, by examining the principles of water displacement, Archimedes was able to prove that a crown was not made of gold (as it was fraudulently claimed) by its density and buoyancy.
The earliest account of fingerprint use to establish identity was during the 7th century. According to Soleiman, an Arabic merchant, a debtor's fingerprints were affixed to a bill, which would then be given to the lender. This bill was legally recognized as proof of the validity of the debt.
The first written account of using medicine and entomology to solve (separate) criminal cases is attributed to the book Xi Yuan Ji Lu (洗冤集錄, translated as "Collected Cases of Injustice Rectified"), written in 1248 China by Song Ci (宋慈, 1186-1249). In one of the accounts, the case of a person murdered with a sickle was solved by a death investigator who instructed everyone to bring their sickles to one location. Flies, attracted by the smell of blood, eventually gathered on a single sickle. In light of this, the murderer confessed. The book also offered advice on how to distinguish between a drowning (water in the lungs) and strangulation (broken neck cartilage).
In sixteenth century Europe, medical practitioners in army and university settings began to gather information on cause and manner of death. Ambrose Paré, a French army surgeon, systematically studied the effects of violent death on internal organs. Two Italian surgeons, Fortunato Fidelis and Paolo Zacchia, laid the foundation of modern pathology by studying changes which occurred in the structure of the body as the result of disease. In the late 1700s, writings on these topics began to appear. These included: "A Treatise on Forensic Medicine and Public Health" by the French physician Fodéré, and "The Complete System of Police Medicine" by the German medical expert Johann Peter Franck.
In 1775, Swedish chemist Carl Wilhelm Scheele devised a way of detecting arsenous oxide, simple arsenic, in corpses, although only in large quantities. This investigation was expanded, in 1806, by German chemist Valentin Ross, who learned to detect the poison in the walls of a victim's stomach, and by English chemist James Marsh, who used chemical processes to confirm arsenic as the cause of death in an 1836 murder trial.
Two early examples of English forensic science in individual legal proceedings demonstrate the increasing use of logic and procedure in criminal investigations. In 1784, in Lancaster, England, John Toms was tried and convicted for murdering Edward Culshaw with a pistol. When the dead body of Culshaw was examined, a pistol wad (crushed paper used to secure powder and balls in the muzzle) found in his head wound matched perfectly with a torn newspaper found in Toms' pocket. In Warwick, England, in 1816, a farm laborer was tried and convicted of the murder of a young maidservant. She had been drowned in a shallow pool and bore the marks of violent assault. The police found footprints and an impression from corduroy cloth with a sewn patch in the damp earth near the pool. There were also scattered grains of wheat and chaff. The breeches of a farm laborer who had been threshing wheat nearby were examined and corresponded exactly to the impression in the earth near the pool.
Forensic science in the media
Sherlock Holmes, the fictional character created by Sir Arthur Conan Doyle in works produced from 1887 to 1915, used forensic science as one of his investigating methods. Conan Doyle credited the inspiration for Holmes on his teacher at the medical school of the University of Edinburgh, the gifted surgeon and forensic detective Joseph Bell.
Decades later, the comic strip, Dick Tracy also featured a detective using a considerable number of forensic methods, although sometimes the methods were more fanciful than actually possible. Popular television series focusing on crime detection, including CSI: Crime Scene Investigation, CSI: Miami, and CSI: NY, depict glamorized versions of the activities of 21st Century forensic scientists. These related TV shows have changed individuals' expectations of forensic science, an influence termed the "CSI effect".
Forensic chemistry
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Forensic chemistry applies the principles of chemistry to law enforcement. Some forensic chemists may deal with explosives or poisons. The bulk of most forensic chemists work is on the analysis of controlled substances. According to federal and state laws an accurate net weight and positive identification of a substance must be obtained before a person can be tried for its possession, distribution or manufacturing. State and local regulations can vary, but in general an analysis must be accomplished based on certain weight criteria. After the weight is obtained the chemist may perform presumptive testing using chemical reagents that cause a color or odor change. The result of the presumptive tests give the chemist clues that guide what type of further testing is required.
For the definitive identification of a substance there are several analytical instruments a chemist can use. One instrument is the gas chromatograph-mass spectrometer (GCMS), which is actually two instruments that are attached. The gas chromatograph is essentially a very hot oven holding a hollow coiled column. A drug sample is diluted in a solvent (e.g.: chloroform, methanol) and is injected into this column, the solvent will evaporate very quickly leaving the drug to travel through the column. The amount of time it takes the drug to travel through the column to a detector is recorded and compared to a known drug. (e.g. cocaine, methamphetamine, heroin, etc.) Gas chromatography alone is only a tentative identification. Once the drug has passed the detector it is sent into the mass spectrometer. A mass spectrometer identifies prominent ions of a drug. It accomplishes this by bombarding the drug with electrons, thus breaking it into its specific ions. This process is also recorded and the results are compared to the known drug.
Another instrument used to identify controlled substances is Fourier Transform infrared spectrophotometer (FTIR). The FTIR records the bending and stretching of molecular bonds that are exposed to infrared light. The molecular bonds of all compounds react differently and create unique patterns upon exposure to a beam of infrared light. The unique pattern created is known as the fingerprint for that drug. As with the GCMS the results of the FTIR are compared to a known drug sample, thus producing a definitive identification.
Forensic identification
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Forensic identification is the application of forensic science and technology to identify specific objects from the traces they leave, often at a crime scene).
Persons can be identified by their fingerprints, from traces of their DNA by DNA fingerprinting, from their teeth by forensic odontology, from a photograph or a video recording by facial recognition systems, from the video recording of their walk by gait analysis, from an audio recording by voice analysis, from their handwriting by handwriting analysis, from the content of their writings by their writing style (eg. typical phrases, factual bias, and/or misspellings of words), or from other traces using other biometric techniques.
Firearms can be identified by ballistics from the marks on the bullets they fired and on the bullet cartridges.
Documents are characterized by the composition of their paper and ink.
Typewriters can be identified by minor variations of positioning and wear of their letters.
Paper shredders can be potentially identified in a similar way, by spacing and wear of their blades.
Color copiers and maybe some color computer printers steganographically embed their identification number to some printouts as a countermeasure of currency forgeries.
Copiers and computer printers can be potentially identified by the minor variants of the way they feed the paper through the printing mechanism, leaving banding artifacts. [1] [2]

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