Forensic Detection: Part One

It can be said that the 20^th century was a century of science, much of which was dedicated to the capture of criminals. The category of science that accomplishes this is known as forensic science. For hundreds of years, scientists and law enforcement agencies have been working together to bring some of the most heinous criminals and murderers to justice. Forensic science has been around since the mid-1700s, but only within the last century has it become more systematic and methodical. Profound breakthroughs have been made in the areas that comprise forensic science. Experts are now using DNA, ultraviolet light, spectrographs, lasers, computers, blood grouping and neuron activation analysis to link crimes and people. There are several sub-divisions of forensic detection. This article will discuss the first five, which are: ballistics, cause of death, disputed documents, DNA typing and explosives.

In terms of criminal investigation, ballistics has become known as the study of bullets and firearms. It involves the analysis of bullets, the weapons from which they emanated and the impact with which they was released. As early as the 15^th century, grooves were being produced in the barrels of firearms to cause the bullet to spin. This process is known as rifling and is designed to improve the aim and accuracy of the shot. Rifled weapons imprint a unique pattern of grooves, indentations and scratches onto each bullet that is fired from it. It is impossible to create two identical barrels. Ergo, bullets fired from different weapons will retain different markings and bullets fired from the same weapon will retain similar markings. Experts are easily able to determine whether or not certain bullets were fired from the same gun based on the striations present on the bullets. The first use of firearm evidence to identify a criminal occurred in England 1835. The markings on a bullet that was retrieved from the victim matched a bullet mold that belonged to the suspect. In 1902, ballistics was first used in a court of law. Expert Oliver Wendell Homes test-fired a bullet from the alleged weapon and matched the markings to bullets that were found at the crime scene.

Several questions arise that need answering when a dead body is discovered. It is pertinent to know who the person is, how long ago he/she died and what was the cause of death. Determining the cause of death is highly important, as it will determine whether or not criminal activity was involved. For instance, if a person died from an illness or natural causes, a criminal investigation is not necessary. It is the burden of the forensic pathologist to take on the grim task of determining the cause of death of an individual. Sometimes the cause is readily apparent, other times it is necessary to thoroughly search for it. The process by which the cause of death is determined is known as a necropsy (or autopsy). This is a post-mortem examination of the body that is usually performed for legal or medical reasons. According to United States Law, the cause of death can fall into one of four categories: accidental, natural, homicidal or suicidal. There are two phases of the autopsy: the external examination and the internal examination. Once the body is received at the medical examiner's office, it is photographed and the pathologist observes the attire and position of the body. Any external residue is collected and Ultraviolet light is used to search the body. Samples of the hair and nails are then taken. The body is then sent to be radiographically imaged. The body is undressed and any wounds are examined. The body is cleaned, weighed and measures. The pathologist then makes note of the race, gender, eye/hair color and any distinguishing traits (scars, birthmarks, etc...). At this point, the internal examination begins. The chest cavity is opened via a Y-shaped incision. The organs are removed and weighed. The body is thoroughly examined for any wounds or indicators of the cause of death. A great variety of tests are performed to determine the presence of toxic substances. The brain is examined and the body is then reconstructed.

The next aspect of forensic detection is disputed documenting. This is mainly used in fraud investigations, but has been applied to other forms of criminal activity. Many serial killers enjoy taunting the media and authorities via written messages. It is in cases like these that disputed documenting is applicable. This type of detection is divided into two sub-categories: handwriting and the veracity of the document itself. Everyone's handwriting fluctuates on a daily basis. Something that you wrote ten years ago may look nothing like something you wrote yesterday. Experts are able to see beyond these shallow inconsistencies and notice the unique style and underlying patterns. This allows the expert to determine whether or not multiple documents were penned by the same person. The document itself is comprised of ink and paper. Thin-layer chromatography is used to analyze ink samples. The Bureau of Alcohol, Tobacco, and Firearms maintains a collection of over three thousand ink chromatograms for comparison and reference purposes. The International Ink Library is maintained by the Secret Service of the United States and contains information pertaining to the chemical composition, formulation and dating of over six thousand different types of ink. To prevent inaccurate dating of ink, ink manufacturers are required to ix a trace dye into the ink; the trace dye is altered on a yearly basis. Through Electrostatic Detection Apparatus (ESDA), it is possible to determine whether or not a certain document has been altered or tampered with. The document is placed upon an electronically charged slab of metal. It is then covered with a thin plastic film. Photocopier toner and glass beads are applied; they stick to the electronically charges areas of the document. The resulting images are compared to the original document and inconsistencies are then detectable.

The fourth aspect of forensic detection is DNA typing. In 1911, a biochemist by the name of Phoebus Levene discovered that each cell possessed a nucleus, which contained nucleic acid. He observed that there were two types of nucleic acid: deoxyribonucleic (DNA) and ribonucleic (RNA). DNA is a set of unique instructions that is responsible for the genetic composition of each individual. In the 1950s, it was theorized that since everyone is different, everyone must possess different sequences of DNA. The four components that comprise DNA were isolated; they were: adenine, cytosine, guanine and thymine. DNA is a sequence of these four components arranged in a double helix pattern. In the sequence, adenine and thymine are always joined together, as are cytosine and guanine. Experts are able to analyze DNA sections to determine if the DNA came from a specific individual. Once the DNA is extracted, an enzyme is mixed into it, causing it to separate at certain sections. The fragments are place in an electrically charged gel. The smaller the fragments are, they faster they move through the gel. Ergo, the sections arrange themselves in size order. They are lifted with a radioactively treated membrane. X-ray photographs of the show parts of the DNA, arranged in a bar code pattern. The prints are compared and similarities are noted. DNA is possibly the most significant tool used in forensic detection, second only to fingerprinting.

The last topic that will be covered in this article is explosives and fire. It is not uncommon for a criminal to attempt to set fire to his/her crime scene in an attempt to destroy evidence. Many murderers seem to believe that incinerating a corpse will eradicate it. Contrary to popular belief, human bodies are highly impervious to fire. It would take extreme temperatures to destroy the teeth and bones of a human body. Experts search the site of the conflagration for any telltale signs of what caused the fire. Un-detonated explosives can often be found near the source of the blaze. Samples are taken of all porous materials in the vicinity. These samples are examined for traces of explosive residue. The debris is then categorized and cleaned using acetone. Depending on the type of material, different types of chromatography are used to analyze and identify the explosive material. When gas chromatography is used, the debris is vaporized and sent down a tube. In the tube, the compounds separate. Each of the different compounds settles at the bottom of the tube at varying rates. This is known as the retention time. The retention time of the components is then compared to a table, which cites the retention times of various chemicals. The experts are then able to identify the present chemicals. There are some components that will become obliterated if they are vaporized. For these, liquid or thin-layer chromatography is used. When using the latter, a glass slide is created: the sample on the bottom and silica gel on the top. The slide is partially submerged in a fluid, which separates the components. Since the results are colorless, it may be necessary to use ultraviolet light or a reagent to view the differences.

The next article will cover the 6^th through tenth aspects of forensic detection. These are: fingerprinting, anthropology, odontology, psychological profiling and identification of remains.