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Forensics and Evidence
Transcript of Forensics and Evidence
Characteristics of ammunition, components, and residue are all examined so that matches can be found.
Bullets are never removed from their hole. The whole surrounding surface is cut out instead.
Gunshot residue (GSR) that is on the hands or face needs to be taken within six hours so it can be sent to a lab that can compare it with the target residue.
When a tool is made and afterwards used, tiny nicks and chips began to form on it. This gives the tool unique characteristics on its blade and edges. Tools used in crimes may also pick up traces of substances with which they came into contact.
At breaking and entering crime scenes, robberies, and other crimes where tools were involved, tool marks can be left and hence found by investigators.
A fingerprint may conclusively can identify both suspects and victims present in a crime because everyone has unique fingerprint patterns.
There are databases like the AFIS (Automated Fingerprint Identification System) are available for quick computerized searching on the national, state, and local level.
There are three types of fingerprint patterns, which are arches, loops, and whorls. They all have individual patterns since everyone has unique fingerprints.
Unit 17 Notes on Forensics and Evidence
Types of Evidence
Testimonial evidence: witnessed accounts of the incident or crime
Physical evidence: material items that would be present at the crime scene or on the victims of the crime. These items are used to prove or disprove the facts of the crime.
Trace evidence: physical evidence that is found at the scene of the crime. It is found in small, but measurable amounts. This type of evidence can be used to identify a victim or suspect of the crime or determine how the crime was committed. Edmund Locard recognized the importance of this evidence in 1910. Locard was the director of a crime laboratory (this first ever) in Lyon, France. The Locard's Exchange Principle says that "with contact between two items, there will be an exchange."
Chemical composition is determined by examining the paint with microscopes and other analytic instruments.
In an accident paint can be transferred from one vehicle to another. Paint chips at the crime scene can be used to find out the make and model of the vehicle. The majority of paint evidence that is submitted to a lab will come from hit-and-run automobile cases.
A tool can be placed at a crime scene from paint that is transferred from a window to the suspect's tool in a break and entry.
The type of explosive that was used in the crime can be determined by examining powders and exploded/unexploded devices.
A sample of the explosive debris can be submitted to the Trace Unit once the Bomb Squad makes sure that the device is safe. The items submitted are then analyzed with chemical spot tests and analytical instrumentation to determine their chemical make-up. This is used to determine what type of explosive was used.
These results can then be compared to any other evidence found in the suspect's possession.
Fragments of glass can become embedded in a victim's hair or clothing in car accidents. Suspects commonly get class fragments on the clothing when involved in a break and entry.
Glass particles can be compared with other particles that are found at the crime scene to determine if the glass particles have common origins.
The properties of glass tint, thickness, UV florescence, density, and refractive index can all be used to match a glass sample to glass that is found at the scene of the crime.
Reconstructing a pane of glass can help when trying to determine the direction of the impact or sequence of impacts.
This form of evidence can possibly reveal where a person has been, where they live, where they work, and/or if they have pets.
Alibi soil samples are taken in a lot of criminal investigations with the majority of the soil samples being taken from the top surface of the soil in small amounts.
Other debris that resides within the samples can tell where a person has been outside.
Semen, saliva, or sweat is usually found to be in splatters, drops, or stains. These fluids can also be found fresh, coagulated, or in dried form.
Each form of these fluids has its own certain method of being collected and preserved.
Bodily fluids like vomit can be found at crime scenes and be used to test alcohol, drugs, and poison. Cigarette butts may contain saliva which has dried. Semen that contains sperm cells is particularly valuable for DNA analysis.
There are 150 proteins, 250 known enzymes, and many more antigens that reside within the blood.
Investigators can usually estimate the time a crime occurred from observing how dry the blood found at the crime scene is.
The shape of the blood when found at the crime scene (pool, drops, stains, or splashes) can provide important clues to show what happened, as well as the location, and description of the bloodstains.
Blood evidence is often times used to eliminate a pool of suspects of the crime.
Wounds can normally be matched to weapons, tool marks on weapons, or at least on weapons' sizes, shapes, and lengths.
Analysis of wound patterns is a special technique that the majority of the time provides clues on how a crime was committed by using the subject's characteristics (whether the subject is left-handed, right-handed, height, etc.).
Shoe prints/Tire prints
Impressions from crime scenes that raise questions can be photographed, lifted, or cast with dental stone so that they can be compared to suspects' shoes or tires.
Impressions may be three-dimensional when they are left in substances like snow or soft soil. They can also be two-dimensional when a impression that is dirty, bloody, or other type is left on a hard surface.
Impressions made by footwear can lead to the identification of suspect because of the treads from their shoes that they left at the crime scene. Treads from shoes are worn down to each person's personal walking style making them unique. There may also be scratches, nicks, or cuts that have been made accidentally and are left on the the bottom of the shoe.
Tires undergo the exact same changes over time that make them each unique too.
When an object breaks, tape is torn, or an object is cut there are two unique edges that are formed as a result. These edges can be compared by the naked eye and they can be put under higher magnification to see if they fit together (like the pieces of a puzzle) making them part of the same exact object.
In a case where the edges do fit together they are then said to physically match each other and the investigators know that the two objects were one object in the past.
Forensic anthropologists analyze skeletal remains that are found so that they can determine the four essential characteristics of a victim. These four characteristics are age, sex, race, and stature.
The first step when analyzing bones is determining whether they are animal or human. After that the next step is finding out the sex of the victim. The innominate bone that makes up the pelvis gives the most definitive traits as to the gender of a person. The humerus or the femur can also be used and an analysis of the skull of the person can give investigators clues about what the sex of the person is.
Through analyzing the development of the teeth, bone growth, and length of certain bones like the femur the age and stature (height) of a victim can be determined.
Through analyzing the skull for characteristics that are common among people of different races the race of a victim can be determined.
Everyone has a specific style of handwriting and the majority of printers also have a specific printing style. The styles of handwriting and ink patterns created by printers can be be compared to match documents to a certain suspect.
Paper chromatography is used in analyzing the ink by separating the ink into different components or colors.
Each one of the thirty-two teeth in every human is unique due to differing ages and wear
Bites can reveal how fast the offender subdued the victim and can most of the time be matched to dental records.
Hair and fibers can be transferred from the suspect of the suspect's clothes to the victim's and the other way around. An example of this would be a pedestrian who is hit by a vehicle may leave hairs and fibers on the suspect's vehicle's bumper or carpet fibers that become attached to a suspect's shoes.
Hair which has roots may give individual DNA evidence.
Hair has certain characteristics too. There are 14 individual elements that can be seen in a sample of hair.
Fibers are normally collected from clothing, carpets, furniture, beds, and blankets.
There are more than a thousand known fibers and there are several thousand known formulas of dye.