Forensic Science and Evidences


Forensic science is a complex and critical part of solving today’s legal affairs, from serious matters like manslaughter to the evaluation of parentage of a child, it has a place almost anywhere. Forensic science is important because it provides concrete, undeniable evidence. I will cover the history of forensic science and compare past techniques with modern techniques. Then I will outline the activity of forensic science throughout the government and how forensic data is analyzed in a lab. After that I will further explain the many subdivisions of forensic science and their specific roles.

The History of forensic science

Forensic has come very far over the past two hundred years. It has advanced from basic eyewitness account to the analysis of DNA. Two hundred years ago, criminal investigation was very primitive. If a crime was committed, detective would have to rely on confessions, eye witness accounts and the most obvious of clues. When investigating a crime scene two hundred years ago the evidence would have been contaminated and any obvious evidence may have been stolen or lost. Although today’s methods are very advanced, forensic science has been around for thousands of years, fingerprinting being the earliest known form that was developed and used the the ancient chinese. Many years later in 1892, Sir Francis Galton established a system for identifying fingerprints. Soon after, others began to develop other methods of identification for fingerprints. In 1896, Sir Edward Henry developed a new way to analyze fingerprints by examining certain characteristic such as pattern, direction and flow. Careful examination and identification of bullets are first recorded in 1835 by Henry Goddard. Goddard used physical analysis to connect a bullet back to a murder weapon. A more exact method was used in the 1920s by Calvin Goddard who created a comparison microscope so match bullets to their shell casings. Gunshot residue detection was later developed in the 1970s with the help of electron microscopes. In the development of forensic chemistry, chemist James Marsh created a way to test for arsenic which was later used in a 1836 murder trial. A century later Karl Lan classified human blood groups and later earned a nobel prize for his work. The advancements that we made in a small amount of time is truly remarkable. From confessions to analyzing blood types, there seems to be an endless amount of knowledge to come.

Criminal Investigation

Crime scene investigators purpose is to collect and examine any evidence left at a crime scene. They look for things like body fluids, fingerprints, hairs and fibers, and other trace evidence. When collecting these, several different methods and materials are used to do so. Trace evidence includes things such as paint and gunshot residue, drugs, glass, and chemicals. Clothing is collected from the victim and anyone else who was present at or near the crime scene and the clothing is to be sealed in a paper bag and taken to a lab to be tested. If the crime was gun related then the clothing will be tested for gunshot residue. If any drugs or unknown powdered substances are found at the scene then it will be collected with a knife or blade, sealed in separate, sterile evidence containers or bags and sent to the lab for identification. Any hair found is sent to DNA testing lab and unknown substances and drugs go to a chemistry lab.

In some cases body fluids are found at the crime scene. Bodily fluids can be saliva, semen, blood or vomit. If blood is found on the body of the victim or any cloth then that will be collected and sent into a lab for possible DNA analysis. There are many tools and materials involved in collecting body fluids from a crime scene. Some of them include scissors, tweezers, a scalpel, luminol, smear slides, UV lights, and sterile cloth. If any hairs or fibers are found at a crime scene then they will be collected using tweezers, combs or vacuums and sent into a lab for analysis. In the event of a rape case, if the victim is still alive then they will be taken to a hospital and examined for any fibers and hairs that could be evidence. Any fibers or hair found at the scene would be compared to fibers or hair of a suspect. DNA analysis can be used to eliminate suspects and to identify if the hair is from a human or an animal. Through DNA analysis a person’s race can be identified from a single human hair.

Fingerprints are also a large clue in a crime scene. A fingerprint can be left behind due to visible fluids like blood or ink, imprinted in something soft and malleable like a clay or wax, or can be from the natural oils that naturally accumulate on everyone’s fingers. Investigators might use brushes, chemicals, tape, a magnifying tool, or other materials to collect these prints for evidence. Prints can be left on paper, wood, plastic, cardboard, metal and other surfaces, both porous and nonporous. When a fingerprint is found on a nonporous surface a powder, often a black or a silver powder, is gently brushed over the print until it is visible, then lifted with tape and transferred to a fingerprint card and submitted to evidence. When a fingerprint is found on a porous surface, chemicals like silver nitrate or iodine are sprayed onto the print until visible.

Footprints may be found at or around a crime scene. If a footprint or an impression from a shoe is found an investigator will make a casting material and make a cast from the print. Any dirt left on the cast when it is removed is not brushed off but rather sent into a lab for analysis. Tool marks from tools used at a crime scene may also be found. It may be an impression- a tool mark that is created without any back-and-forth movement- or it may be a striation- a tool mark with a series of parallel lines cause by a back-and-forth movement. Attempting to match a tool to an impression is rather unreliable and it is more reliable to make a definite match with a striated mark.

When an investigator finds any firearms at a crime scene, they need to follow a specific routine to preserve the evidence. Gloves are worn and the firearm is pick up by the barrel and placed into an evidence bag to be sent to a lab for testing. Forensic scientists can then examine any casings found and match them to a weapon or they can examine serial numbers found on the firearm. By using a laser trajectory kit, investigators can use any bullet holes in a victim or surface to determine the location and height that the bullet was fired from. If the bullet or casing is stuck in a wall or other material then a section of it will be removed instead of attempting to dig it out, which ruins the evidence.

When documents are found such as letters, planners, calendars, books, journals, suicide notes, etc. they are collected and preserved. A lab may be required to reconstruct demolished evidence that may have been burned or torn apart. These documents are recorded and analyzed for handwriting samples, forgery, and what was used to print or write the document.

Whenever any type of evidence is found at a crime scene, and investigator must photograph it, log it, recover and then tag the evidence. But how is all of this evidence discovered? When examining a body or corpse, investigators look for many things such as stains, wrinkling or bunching of clothing that could indicate dragging, defense wounds, bruises, cuts, any obvious missing items, direction of the flow of blood, insects, etc.. After moving the body, the other side of the corpse is examines in the same manner and then the bod temperature and the room temperature are taken to estimate the time of death. Fingerprints of the body will be taken and placed into evidence. Once the conditions of the body are documented, then the body is covered in a white cloth and transported to a morgue for an autopsy. To efficiently and carefully find and collect evidence, investigators use several different methods of examination of a crime scene. Investigators may use the inward spiral search method where they start from the perimeter of the crime scene and slowly work their way towards the center of the scene in a spiral pattern. Another method is the outward spiral where investigators might start from the center of a crime scene or from the location of a body and slowly and meticulously work their way to the edges of the crime scene in a spiral pattern. If there is a team of investigators, they may use the parallel, grid, or zone search methods. The parallel search method requires the team of criminal investigators to line up and walk in a straight line from one side of the crime scene to the other. The grid search is similar but requires the team to repeat the method from an adjacent side. In a zone search, investigators divide the room into different sections, then search each section thoroughly and then move onto the next section.

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