Module 2 Trace Evidence Flashcards
trace evidence
Evidence that cannot be seen clearly by the human eye.
The importance of trace evidence to crime scenes should not be underestimated; and often is crucial to the investigation is significant and should not ignored.
Common trace evidence includes human hair, animal hair, carpet fibers, clothing fibers, glass fragments, and paint fragments.
Can be easily overlooked if a crime scene isn’t carefully analyze
Locard Exchange Principle, which is the basis for the study of trace evidence
states that when an individual comes into contact with another person or a specific location, small debris from that person is left behind
Microscopic trace evidence can reveal much information about the suspect.
For example, the micrograph photo can show a single human hair and indicated that the person had lice
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When forensic experts examine a piece of trace evidence under the microscope, they will first identify it.
After it has been identified, investigators attempt to individualize it.
To do this, they determine if the evidence is from an organic (natural) source or inorganic (synthesis/man-made) source.
However more evidence is needed to charge and convict a suspect
Collection of Trace Evidence from a Crime Scene
Securing the scene is usually managed by
officers who arrived first
Once the area is secure victims, suspects, and witnesses are then questioned.
Ensuring that no one leaves or comes into the scene is important .
Observations of the Crime Scene Before any evidence is collected, the crime scene is photographed or videotaped in its unaltered state
Anything from the crime scene is photographed several times from different angles.
Photo tents are used to provide a label and perspective in size.
set beside objects photographed at scene
is a tedious task
J-Lifts are essentially (very sticky tape that adhere to microscopic evidence).are used to lift trace evidence from bodies/objects found at scene.
evidence can then be easily transferred to slides and observed under the microscop
Collection of Trace Evidence from a Crime Scene - Part II 3.
Collection of Trace Evidence Normally, one officer is in charge of supervising the collection of evidence to ensure it is completed efficiently and thoroughly.
police investigators often wear ‘protective suits’ to prevent anything on their body, such as hair, fibres, sweat, and saliva, from combining with and/or contaminating the evidence collected.
Although rarely seen on television, police investigators often wear ‘protective suits’ to collect evidence.
Each piece of trace evidence is properly labelled with date, time, case number, and brief description.
Collecting Trace Evidence at Home One of the most useful tools that forensic experts use to collect trace evidence is a common household item - clear tape.
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Hair is one of the most common types of microscopic physical evidence found at crime scenes.
Microscopic hair evidence combined with DNA analysis is very strong corroborative evidence in a criminal case.
Hair sample evidence is often found after an incident of physical violence such as assault, sexual assault, and homicide.
However, DNA analysis is time-consuming, expensive, and difficult, and it is usually only used in the investigation of serious violent crimes such as kidnapping, manslaughter, murder, and sexual assault.
Hair is a valuable piece of evidence because it does not degrade rapidly.
Defense lawyers may question this individualization of hair in court with the argument that many humans share similar hair colours and textures.
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Long hair often is from a woman; however, many males have long hair.
Human Hair vs.
Human and Animal Hair Hairs from various parts of the body differ in their structure, texture, length, and colour.
Also, human hairs tend to be slightly darker near the exterior of each hair (cuticle) while animal hairs tend to be darker near the middle (medulla).
Various strands of colour-treated hair.
The next section identifies and compares some of the unique features of various types of animal hair with human hair.
The roots will differ from the rest of the hair strand (likely darker in colour).
Hair samples from a suspect must be taken from all areas of his/her body for accurate comparison.
Humans do not shed these hairs as often as they shed hairs from the head.
Colour-treated hair exhibits little colour variation in the medulla region (middle of hair strand).
Human hairs generally tend to be consistent in colour throughout the length of the hair shaft, but the colour in animal hairs is found in bands randomly throughout the hair.
Head Hair This is the longest of all body hairs; only beard hairs can grow as long.
They are usually darker than head and body hair.
Below are descriptions of four types of human hair that likely will be found at a crime scene.
At least ten or twelve hairs from each possible location should be taken for comparison purposes.
Pubic Hair Hairs from the pubic area or genitalia are usually dark (brown or black is most common), very curly, stiff, and thicker and longer than body hair and eyebrow or eyelash hair (1-2 cm).
Hairs from the head often have cut or split tips, and other body hairs do not.
They are typically arc shaped and tend to be lighter colour than head and eyebrow or eyelash hair.
Hair from the head will likely be sun-bleached or colour-treated.
Many humans own domesticated animals as pets or for farming purposes; therefore, if a unique animal hair is found at a crime scene and can be linked to a victim or suspect, it can help establish a case against the suspect
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Forensic scientists are interested in looking at the length, diameter, and internal structures of hair evidence.
In particular, some of the internal structures (tip variation, root variation, cortex colour, medullary index, and medullary shape) are unique among humans and animals.
The best way to observe the internal structures of hair is with a light microscope.
The hair root lies below the epidermis layer of the skin and is similar in appearance to a tulip bulb with its rounded shape.
Gross Anatomy: The three parts of a hair are the root, tip, and shaft.
The only part of the hair that requires oxygen and nutrients is the hair root because the cells in the rest of the hair are made of non-living keratin.
Rounded (club) root
The root of a human hair that falls out naturally is club- shaped whereas the shape of animal roots varies.
Follicle-attached root
If the follicle is attached to the root (the follicle looks like transparent skin around the root), the hair was forcibly removed, perhaps during a violent struggle.
Dark band root
A dark band near the tip of the root likely indicates the hair was shed after the person died.
Frayed root
This indicates the hair likely came from a cat.
Spade-shape root
This indicates the hair likely came from a dog.
Wineglass-shaped root
This indicates the hair likely came from a deer.
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. The Hair Tip
The tip of the hair can be distinguished from the root as it will never have any skin directly attached to it. This part of the hair is not directly attached to the body and is found furthest away from the scalp.
slightly rounded tip indicates what?
individual has not had a hair cut in a long period of time (ie. likely > 4 weeks since last cut).
linear/straight tip indicates what?
individual has recently had a hair cut.
blackened/frayed tip indicates what?
individual has come into close contact with flames/high heat (see photo to the right).
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The Hair Shaft The shaft of the hair is the region found in between the root and the tip.
The three parts of the hair shaft include the cuticle, cortex, and medulla.
The outermost layer of the hair shaft is called the cuticle which is made up of a layer of scales covering the outside of the hair shaft
Imbricate cuticle
Scale pattern found in all human hairs and some animals
Coronal cuticle
Scale pattern found in the hair of small rodents (ie. mouse, rat, vole) and bats
Spinous cuticle
Scale pattern found in the hair of minks, seals and cats.
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The middle region of the hair shaft is called the medulla. The medulla shows great variation among humans and animals. Under high magnification, the basic internal structure of the medulla is referred to as the medulla index. The major types of medulla indices include unisereal, lattice, multisereal, vacuolated and amorphous (fragmented & continuous).
The best way to differentiate between human and animal hairs is by looking at the medulla. In human hairs, the medulla has no distinct structure (amorphous), whereas in animal hairs, the medulla is found in a well defined pattern (unisereal, lattice, mutlisereal, vacuolated). Also, the medulla in human hair is narrow and takes up little space, whereas the medulla in animal hair is wide and takes up more space
unisereal medulla
Found in hair from a cat or a rabbit.
vacuolated medulla
Found in hair from a dog, a red fox or cattle.
lattice medulla
Found only in hair from a deer or elk, goat.
multisereal medulla
Found in a rabbit or a chinchilla
amorphous medulla
Found in human hair. Black human hair tends to be continuous, while all other hair colours tend to be fragmented.
A fibre is?
the smallest unit making up the fabric of clothing, drapery, furniture, and carpet. A fibre tends to have a thin diameter and long length
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Fibres are a form of trace evidence often found at crime scenes where the suspect(s) and victim(s) have been in physical contact, such as assault or homicide. Fibre evidence can also be exchanged between a hit-and-run victim and the vehicle that caused the collision. It can be left at the site of the collision in clothing fibres and fragments of glass or paint. Also, fibres from a suspect can become snagged in a screen or glass broken during a break-and-enter.
A suspect may be placed at the crime scene by locating fibres from objects such as carpet, drapery, and furniture from the crime scene similar to those from the victim’s clothing or upon the clothing of the suspect. Fibres found at the crime scene that are similar to the suspect’s clothing can be incriminating
What can Fibre Evidence Can Help to Prove
- the occurrence of physical contact.
The discovery of a single fibre that has been transferred between the suspect’s clothing and the victim’s clothing increases the likelihood that these two people were in physical contact with one another. Better yet, many fibres found on clothing or fabric from the suspect, victim, or crime scene dramatically increase the likelihood that contact occurred. Every fibre is considered to be an independent piece of evidence, and numerous pieces of evidence help destroy the argument that the contact is a simple coincidence. - the type of contact that occurred.
Violent physical contact over a lengthy period often results in numerous fibres being exchanged among the suspect, victim, and crime scene.
Fibre Transfer: Primary vs. Secondary
Fibres may be transferred during a crime through direct contact (primary) or indirect contact (secondary). A primary transfer happens when a fibre is exchanged from any fabric directly to a victim’s clothing. For example, a suspect’s hair is found on the victim’s clothing. A secondary transfer occurs when a transferred fibre on the suspect is placed upon the victim. For example, a carpet fibre from a suspect’s home is transferred to the suspect’s clothing and is then transferred onto the victim. Determining whether a fibre was a primary or secondary transfer is important when attempting to re-enact the events of a crime.
Collection & Analysis of Fibre Evidence
After a crime has been reported, fibres must be immediately collected. Investigators must obtain the clothing from a victim and suspect as soon as possible. Little fibre loss occurs if a victim has been found dead but fibres from the victim are easily lost if movement has occurred after the crime. The chances of finding fibre evidence on a suspect more than a day after the crime has occurred is small because movement causes fibres to be lost. Also, the clothing worn at the crime scene may have been washed or discarded. Clothing from a victim and suspect must be carefully handled because fibre evidence can easily be lost.
The first two steps in the microscopic analysis of fibre evidence are the comparison of the colour and diameter of each fibre. If both the colour and diameter are not similar, the fibres in question are not a match. The third step is determining the number of matched fibres found.
- Fibre Colour
When looking at the colour of a fibre, the shade (light or dark) is first determined; then, any unique colour pigments are identified. The microscopic analysis of fibre colour may help to identify the fabric from which it originated. How the colour is applied to a fibre and absorbed by a fibre are important traits to observe. In printed fabrics, the colour is usually applied to the surface so individual fibres have colour on their surface and not throughout the entire strand. In a single colour fabric, each fibre has been dyed so colour will appear throughout the entire strand. Also, the fading and discolouration of a fabric may be helpful as it could help to individualize fibres found. - Fibre Diameter
Both the size and shape of a fibre’s diameter are determined to identify the type of fibre being analyzed-natural or man made. This information helps investigators hypothesize about type of object the fibre came from-clothing, furniture, blanket, carpet, etc. - Fibre Number
The number of fibres on a victim that match fibres from the clothing of a suspect can confirm physical contact. The greater the number of fibres found, the more probable contact actually occurred between these individuals
