Sample essay topic, essay writing: Trace Evidence - 1589 words
Crime scenes are known to have many clues left behind. The obvious would be a the body or bodies, clothing, and sometimes even the murder weapon. While these are great way to solve a case there's another kind of evidence; trace evidence. Trace evidence are small pieces of evidence that are laying around a crime scene. There are many types of trace evidence some of them include metal filings, plastic fragments, gunshot residue, glass fragments, feathers, food stains, building materials, lubricants, fingernail scrapings, pollens and spores, cosmetics, chemicals, paper fibers and sawdust, human and animal hairs, plant and vegetable fibers, blood and other body fluids, asphalt or tar, vegetable fats and oils, dusts and other airborne particles, insulation, textile fibers, soot, soils and mineral grains, and explosive residues. Although these are the most common found elements, they are not the only ones. The Trace Evidence Unit is known to examine the largest variety of evidence types and used the biggest range of analytical methods of any unit. materials are compared with standards or knowns samples to determine whether or not they share any common characteristics.
In this paper I will discuss the different kinds of trace evidence and how crime scene investigaros use it to solve cases and convict criminal. Trace evidence was first discovered by Edmond Locard. Edmond Locard was born in 1877, and founded the Institute of Lyon's Institute of Criminalistics. He is also known for advancing the science of fingerprints. In 1910 he was authorized to start a small forensic laboratory in the Palais de Justice which he directed until 1951.While there he worked on criminal identification methods including poroscopy - the microscopic examination of fingerprints; analyses of body fluids, hair and skin; and graphometry or handwriting analysis. He is the man responsible for coming up with the theory that when two objects come in contact with each other they leave some kind of material matter behind
This theory was later called Locard's Exchange Principle. The idea is that the evidence can be used to associate objects, individuals or locations with one another.' A person typically loses about 100 hairs a day. These hairs may be of evidentiary value to show contact between two people. With an adequate hair standard, a trace chemist will be able to microscopically compare an unknown hair to a standard collection and determine if the unknown hair could have come from the individual under investigation. Hair comparisons can not identify a hair as coming from one individual to the exclusion of anyone else. DNA testing can strengthen any possible association of the hairs.' - Locard. Hair is usually found in unusual amounts when there was a struggle or fight between the victim and suspect or suspects.
Hair at a crime scene is usually found on the floor near whatever was used to commit the crime or the point of impact between the suspect and victim. If a hair is found with the root still intact then DNA can be pulled from it although DNA can also be found from fingernails, toenails, and skin flakes. Hair can tell the investigators many things. For insance, the race of the person, whether they dye their hair or not, the natural color of their hair, and if it simply fell out or alot of force was used to pull it out of the scalp. Fibers are found mostly on clothing, furniture, carpeting, and blankets at a crime scene. The fibers found are usually from either clothing or carpet.
Cross-transfer of fiber evidence usually occurs where person-to-person contact was established. There are well over a thousand known fibers and a few thousand known dye formulas. Every dye formula is registered and available in the database investigators use to compare these small pieces of evidence. Glass from doors, decorations, or windows are usually found on clothing and the soles of shoes. It can also be found on tools, skin, and even the weapon. Different types of glass break and shatter differently as well as have different characteristics when it comes to densities and refractive indexes. Glass can also hold fingerprints which can be very valuable to an investigation as the fingerprints can be taken up on tape and then ran through a database, possibly finding a match and allowing the investigators to find and capture a suspect. Weapons, pray bars, blunt objects, clothing, and shoes are where paint chips from door, walls, and furniture can be found.
In order for paint to chip off there needs to be a pretty serious struggle or a pretty hard force that will chip away at the paint then causing it to land somewhere that the suspect forgot about. The Crime Scene labs have about forty thousand different types of paint in their database. The majority of paint chips are from hit and run cases involving automobiles. Dust and Dirt can determine many things to help an investigation along. It can tell the investigators where a person has been, where they work, where they live, and if they have pets in the house. Most soil samples will come from the top soil and only need to be a little bit over a tablespoon to be processed.
Pollen is also included in this as it is a subtype of dust and dirt Pollen allows the investigators to know if they suspect or victim were outdoors, and if so where they could have been. Firearms that are left behind at a crime scene can be extremely helpful. This evidence includes not only the firearm itself but also the ammunition used in the firearm, componets that make up the firearms, and the residue that comes out when the firearm in question is shot. Bullets are never taken away from where they penetrated. Instead the surrounding area is cut out as to not ruin or contaminate the entrance area. They usually use the science of ballistics to determine most evidence dealing with firearms. Fluids include semen, saliva, sweat, and vomit and are usually found at scenes where drugs, alcohol, and poisons are involved. Fluid evidence can be very helpful as it can contain DNA which will allow the investigators to run it through the database.
Each fluid has to be collected quickly and be rushed to the lab. Investigators often estimate the time of a crime by how dry any blood is. Every one has around ten pints of blood, 150 known proteins, 250 known enzymes, and tons more antigens. The shape of the blood evidence can provide investigators with information as to what may have happened. Blood is most commonly found in pools, drops, stains, or splatter. Blood is also very helpful as it allowed the investigators to eliminate a variety of people as suspects.
When processing a crime scene, blood stains are usually the most detailed when it comes to photographs, notes, and sketching. Blood stain pattern analysis is the most commonly used method of crime scene reconstruction when blood is involved. Footprints and shoeprints are not exactly prints, but impressions on a soft surface, for instance dirt. Shoeprints show individual signs of wear, and are extremely unique since a persons height, weight, and stride pattern can change the wear on the soles of the shoes, and the way the shoeprint turns out. For instance, if someone is pigeon-toed then the shoeprint will show that therefore eliminating all suspects who are not pigeon toed. Investigators like to record shoeprints in their notebooks and sketching, only when it is 100% certain that all trace evidence has been collected do they do a plaster cast of the print. Bite marks are very unique as each tooth in a persons mouth has different wear patterns and its shape and size will be different depending on how old the person is. When someone is bit it allows the investigators to match the bit marks to dental records which can then narrow down the search to a specific person. While tools are made the same way everytime in a factory, the wear and use of the tool can change the way it's blade or edges look. A took also picks up tiny pieces of trace evidence such as metal, and paint while it's being used. This evidence is usually from windowsills and frames, doors, door frames, file cabinets, cash register drawers, or any peice of furniture which may be locked. They then use the small paint chips and metal as evidence and process them the way that individual piece of evidence should be processed. Believe it or not, wounds from a victim are also evidence.