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.
