forensic science: Definition and Much More from Answers.com

Forensic science is a multidisciplinary subject used for examining crime scenes and gathering evidence to be used in prosecution of offenders in a court of law. Forensic science techniques are also used to examine compliance with international agreements regarding weapons of mass destruction.

The main areas used in forensic science are biology, chemistry, and medicine, although the science also includes the use of physics, computer science, geology, and psychology. Forensic scientists examine objects, substances (including blood or drug samples), chemicals (paints, explosives, toxins), tissue traces (hair, skin), or impressions (fingerprints or tidemarks) left at the crime scene. The majority of forensic scientists specialize in one area of science.

Evidence and Trace Examination

The analysis of the scene of crime or accident involves obtaining a permanent record of the scene (forensic photography) and collection of evidence for further examination and comparison. Collected samples include biological (tissue samples such as skin, blood, semen, or hair), physical (fingerprints, shells, fragments of instruments or equipment, fibers, recorded voice messages, or computer discs) and chemical (samples of paint, cosmetics, solvents, or soil).

Most commonly, the evidence collected at the scene is subsequently processed in a forensic laboratory by scientists specializing in a particular area. Scientists identify, for example, fingerprints, chemical residues, fibers, hair, or DNA left behind. However, miniaturization of equipment and the ability to perform most forensic analysis at the scene of crime results in more specialists being present in the field. Presence of more people at the scene of crime introduces a greater likelihood of introduction of contamination into the evidence. Moreover, multi-handling of a piece of evidence (for example a murder weapon being analyzed by many specialists) is also likely to introduce traces of tissue or DNA not originating from the scene of a crime. All this results in strict quality controls imposed on collection, handling, and analysis of evidence to ensure lack of contamination. For example, in DNA analysis it is essential that samples are stored at the correct temperature and that there is no contamination from a person handling a sample by wearing clean gloves and performing analysis in a clean laboratory.

Ability to properly collect and process forensic samples can affect the ability of the prosecution to prove their case during a trial. The presence of chemical traces or DNA on a piece of debris is also crucial in establishing the chain of events leading to a crime or accident.

A growing area of forensic analysis is monitoring non-proliferation of weapons of mass destruction, analysis of possible terrorist attacks or breaches of security. The nature of samples analyzed is wide, but slightly different to a criminal investigation. In addition to the already described samples, forensic scientists who gather evidence of mass destruction collect swabs from objects, water, and plant material to test for the presence of radioactive isotopes, toxins, or poisons, as well as chemicals that can be used in production of chemical weapons. The main difference from the more common forensic investigation is the amount of chemicals present in a sample. Samples taken from the scene of suspected chemical or biological weapons often contain minute amounts of chemicals and require very sensitive and accurate instruments for analysis.

Biological traces. Biological traces are collected not only from the scene of crime and a deceased person, but also from surviving victims and suspects. Most common samples obtained are blood, hair, and semen. DNA can be extracted from any of these samples and used for comparative analysis.

DNA is the main method of identifying people. Victims of crashes or fires are often unrecognizable, but adequate DNA can be isolated and a person can be positively identified if a sample of their DNA or their family's

DNA is taken for comparison. Such methods are being used in the identification of the remains in Yugoslav war victims, the World Trade Center terrorist attack victims, and the 2002 Bali bombing victims.

Biological traces, investigated by forensic scientists come from bloodstains, saliva samples (from cigarette buts or chewing gum) and tissue samples, such as skin, nails, or hair. Samples are processed to isolate the DNA and establish the origin of the samples. Samples must first be identified as human, animal, or plant before further investigation proceeds. For some applications, such as customs and quarantine, traces of animal and plant tissue have to be identified to the level of the species, as transport of some species is prohibited. A presence of a particular species can also prove that a suspect or victim visited a particular area. In cases of national security, samples are tested for the presence of pathogens and toxins, and the latter are also analyzed chemically.

Chemical traces. Forensic chemistry performs qualitative and quantitative analysis of chemicals found on people, various objects, or in solutions. The chemical analysis is the most varied from all the forensic disciplines. Chemists analyze drugs as well as paints, remnants of explosives, fire debris, gun shot residues, fibers, and soil samples. They can also test for a presence of radioactive substances (nuclear weapons), toxic chemicals (chemical weapons) and biological toxins (biological weapons). Forensic chemists can also be called on in a case of environmental pollution to test the compounds and trace their origin. The samples are obtained from a variety of objects and often contain only minute amounts of chemicals.

The identification of fire accelerants such as kerosene or gasoline is of great importance for determining the cause of a fire. Debris collected from a fire must be packed in tight, secure containers, as the compounds to be analyzed are often volatile. An improper transport of such debris would result in no detection of important traces. One of the methods used for this analysis involves the use of charcoal strips. The chemicals from the debris are absorbed onto the strip and subsequently dissolved in a solvent before analysis. This analysis allows scientists to determine the hydrocarbon content of the samples and identify the type of fire accelerator used.

Physical evidence. Physical evidence usually involves objects found at the scene of a crime. Physical evidence may include all sorts of prints such as fingerprints, footprints, handprints, tidemarks, cut marks, tool marks, etc. Analysis of some physical evidence is conducted by making impressions in plaster, taking images of marks, or lifting the fingerprints from objects encountered. These serve later as a comparison to identify, for example, a vehicle that was parked at the scene, a person that was present, a type of manufacturing method used to create a tool, or a method used to break in a building or harm a victim.

An examination of documents found at the scene or related to the crime is often an integral part of forensic analysis. Such examination is often able to establish not only the author, but more importantly identify any alterations that have taken place. Specialists are also able to recover text from documents damaged by accident or on purpose.

Identification. The identification of people can be performed by fingerprint analysis or DNA analysis. When none of these methods can be used, the facial reconstruction can be used instead to generate a person's image. TV and newspapers then circulate the image for identification.

Other Fornsic Scientists

Pathologists and forensic anthropologists play a very important part in forensic examination. They are able to determine the cause of death by examining marks on the bone(s), skin (gunshot wounds), and other body surfaces for external trauma. They can also determine a cause of death by toxicological analysis of blood and tissues.

A number of analytical methods are used by forensic laboratories to analyze evidence from a crime scene. Methods vary, depending on the type of evidence analyzed and information that needs to be extracted from the traces found. If a type of evidence is encountered for the first time, a new method is developed.

Biological samples are most commonly analyzed by polymerase chain reaction (PCR). The results of PCR are then visualized by gel electrophoresis. Forensic scientists tracing the source of a biological attack could use the new hybridization or PCR-based methods of DNA analysis. Biological and chemical analysis of samples can identify toxins found.

Imaging used by forensic scientists can be as simple as a light microscope, or can involve an electron microscope, absorption in ultraviolet to visible range, color analysis or fluorescence analysis. Image analysis is used not only in cases of biological samples, but also for analysis of paints, fibers, hair, gunshot residue, or other chemicals. Image analysis is often essential for an interpretation of physical evidence. Specialists often enhance photographs to visualize small details essential in forensic analysis. Image analysis is also used to identify details from surveillance cameras.

The examination of chemical traces often requires very sensitive chromatographic techniques or mass spectrometric analysis. Four major types of chromatographic methods used are: thin layer chromatography (TLC) to separate inks and other chemicals, atomic absorption chromatography for analysis of heavy metals, gas chromatography (GC), and liquid chromatography (HPLC). GC is most widely used in identification of explosives, accelerators, propellants, and drugs or chemicals involved in chemical weapon production, while liquid chromatography (HPLC) is used for detection of minute amounts of compounds in complex mixtures. These methods rely on separation of the molecules based on their ability to travel in a solvent (TLC) or to adhere to adsorbent filling the chromatography column. The least strongly absorbed compounds are eluted first and the most tightly bound last. By collecting all of the fractions and comparing the observed pattern to standards, scientists are able to identify the composition of even the most complex mixtures.

New laboratory instruments are able to identify nearly every element present in a sample. Because the composition of alloys used in production of steel instruments, wires or bullet casings is different between various producers, it is possible to identify a source of the product.

In some cases chromatography alone is not an adequate method for identification. It is then combined with another method to separate the compounds even further and results in greater sensitivity. One such method is mass spectrometry (MS). A mass spectrometer uses high voltage to produce charged ions. Gaseous ions or isotopes are then separated in a magnetic field according to their masses. A combined GC-MS instrument has a very high sensitivity and can analyze samples present at concentrations of one part-per-billion.

As some samples are difficult to analyze with MS alone, a laser vaporization method (imaging laser-ablation mass spectroscopy) was developed to produce small amounts of chemicals from solid materials (fabrics, hair, fibers, soil, glass) for MS analysis. Such analysis can examine hair samples for presence of drugs or chemicals. Due to its high sensitivity, the method is of particular use in monitoring areas and people suspected of production of chemical, biological or nuclear weapons, or narcotics producers.

While charcoal sticks are still in use for fire investigations, a new technology of solid-phase microextraction (SPME) was developed to collect even more chemicals and does not require any solvent for further analysis. The method relies on the use of sticks similar to charcoal, but coated with various polymers for collecting different chemicals (chemical warfare agents, explosives, or drugs). Collected samples are analyzed immediately in the field in by GC.

A number of instruments used are smaller than ever before, allowing them to be used directly in the field with rapid results. For example, a combined GC-MS analysis device can analyze a sample within 15 minutes directly in the field. The standard laboratory instrument is large with a weight over 100 kilograms, while the portable version is only 28 kilograms. A number of government agencies (for example the FBI) are now armed with the portable instruments and can perform rapid forensic analysis in the field in a time shorter than it would take to transport samples to a forensic laboratory. United States troops are equipped with similar instruments on board some tanks and trucks, in order to quickly determine the presence of chemical or biological weapons on the battlefield

Applications of forensic science. The main use of forensic science is for purposes of law enforcement to investigate crimes such as murder, theft, or fraud. Forensic scientists are also involved in investigating accidents such as train or plane crashes to establish if they were accidental or a result of foul play. The techniques developed by forensic science are also used by the army to analyze the possibility of the presence of chemical weapons, high explosives or to test for propellant stabilizers. Gasoline products often evaporate rapidly and their presence cannot be confirmed, but residues of chemicals, such as propellant stabilizers, are present for much longer indicating that an engine or missile was used.

Further Reading

Houde, John. Crime Lab: A guide for Nonscientists. Rolling Bay: Calico Press, 1998.

Kelly, John F., and Phillip K, Wearne. Tainting Evidence: Inside the Scandals at the FBI Crime Lab. New York: Free Press, 1998.

Saferstein, Richard. Criminalistics: An Introduction to Forensic Science. New York: Prentice-Hall, 2000.

Electronic

American Academy of Forensic Science <http://www.aafs.org.> (7 February 2003).

Consulting and Ducation in Forensic Science. "Forensic Science Timeline." Norah Rudin. <http://www.forensicdna.com/Timeline.htm.>(7 February 2003).

Forensic Science Center, University of California Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94550–9234. (925) 423–1189. <http://www.llnl.gov/IPandC/op96/10/10h-for.html.> (7 February 2003).

Forensic Science Web Pages. 7 February 1997. <http://home.earthlink.net/~thekeither/Forensic/forsone.htm.>(7 February 2003).

National Center for Forensic Science, University of Central Florida 12354 Research Parkway Orlando, FL 32826.(407) 823–6469. <http://ncfs.ucf.edu/navbar.html.> (7 February 2003).

This entry contains information applicable to United States law only.

The application of scientific knowledge and methodology to legal problems and criminal investigations.

Sometimes called simply forensics, forensic science encompasses many different fields of science, including anthropology, biology, chemistry, engineering, genetics, medicine, pathology, phonetics, psychiatry, and toxicology.

The related term criminalistics refers more specifically to the scientific collection and analysis of physical evidence in criminal cases. This includes the analysis of many kinds of materials, including blood, fibers, bullets, and fingerprints. Many law enforcement agencies operate crime labs that perform scientific studies of evidence. The largest of these labs is run by the Federal Bureau of Investigation.

Forensic scientists often present expert testimony to courts, as in the case of pathologists who testify on causes of death and engineers who testify on causes of damage from equipment failure, fires, or explosions.

Modern forensic science originated in the late nineteenth century, when European criminal investigators began to use fingerprinting and other identification techniques to solve crimes. As the field of science expanded in scope throughout the twentieth century, its application to legal issues became more and more common. Because nearly every area of science has a potential bearing on the law, the list of areas within forensic science is long.

Forensic Medicine and Psychology

Forensic medicine is one of the largest and most important areas of forensic science. Also called legal medicine or medical jurisprudence, it applies medical knowledge to criminal and civil law. Areas of medicine that are commonly involved in forensic medicine are anatomy, pathology, and psychiatry.

Many law enforcement agencies employ a forensic pathologist, sometimes called a medical examiner, who determines the causes of sudden or unexpected death. Forensic toxicologists, who study the presence of poisons or drugs in the deceased, often help forensic pathologists. Forensic odontologists, or dentists, analyze dental evidence to identify human remains and the origin of bite marks.

Forensic medicine is often used in civil cases. The cause of death or injury is considered in settling insurance claims or medical malpractice suits, and blood tests often contribute to a court's decision in cases attempting to determine the paternity of a child.

Mental health and psychology professionals have contributed a great deal to the legal understanding of issues such as the reliability of eyewitness testimony, responsibility for criminal behavior, and the process of decision making in juries. These professionals include those with a medical degree, such as psychiatrists, neurologists, and neuropsychologists, as well as individuals without a medical degree, such as psychologists.

Mental health professionals are frequently consulted in civil and criminal cases to help determine an individual's state of mind with regard to a crime, the validity of testimony before a court, or an individual's competence to stand trial or make a legal decision. Their input may also be vital to legal procedures for deciding whether to commit a person to an institution because of mental illness, or to allow a person to leave an institution for those who are mentally ill.

Forensic neuropsychology is a specialized area of forensic medicine that applies the functioning of the nervous system and brain to legal issues involving mind and behavior. Equipped with an improved understanding of how the brain works and influences behavior, neuropsychologists have increasingly been asked to provide testimony to courts attempting to determine whether a criminal act is a result of a nervous system dysfunction. They also testify as to the reliability of witness testimony given by victims of crime, the competency of individuals to stand trial, the likelihood that a condition of mental retardation or brain injury predisposed an individual to commit a crime, the possibility that an individual has verifiable memory loss, and various aspects of dementias and other brain disorders caused by AIDS, head injuries, and drugs, alcohol, and other chemicals.

In civil cases, the work of neuropsychologists has been used to determine whether a defendant's wrongdoing caused a plaintiff's injury. In family courts, neuropsychologists assess brain damage in children who have been physically abused.

Forensic psychologists provide expert testimony that touches on many of the same areas as that given by forensic psychiatrists and neuro- psychologists. In addition, psychologists consult with the legal system on issues such as correctional procedures and crime prevention. In 1962, a U.S. court of appeals issued an influential decision that established the ability of a psychologist to testify as an expert witness in a federal court of law (Jenkins v. United States, 113 U.S. App. D.C. 300, 307 F.2d 637 [D.C. Cir. 1962]). Before that time, expert testimony on mental health was largely restricted to physicians.

Other Areas of Forensic Science

Forensic engineers provide courts with expertise in areas such as the design and construction of buildings, vehicles, electronics, and other items. Forensic linguists determine the authorship of written documents through analyses of handwriting, syntax, word usage, and grammar. Forensic anthropologists identify and date human remains such as bones. Forensic geneticists analyze human genetic material, or DNA, to provide evidence that is often used by juries to determine the guilt or innocence of criminal suspects. Forensic phoneticians deal with issues such as the validity of tape-recorded messages, the identification of speakers on recorded messages, the enhancement of recorded messages, the use of voiceprints, and other aspects of electronic surveillance.

See: DNA evidence.