Forensic Science chapters 11 and 17
compositional differences may exist in the dyes that were ___________________
applied to the fibers during the manufacturing process
forensic hair comparisons involve either __________________
head hair or pubic hair
to initiate and sustain a fire or combustion, the following are required:
- a fuel (vapor) must be present - oxygen must be available in sufficient quantity to combine with the fuel - heat must be applied to initiate the combustion, and sufficient heat must be generated to sustain the reaction
Physical State of the fuel
- fuel achieves reaction rate with oxygen sufficient to produce a flame only when it is in the gaseous state. thus, rusting will not be accompanied by a flame. - a liquid burns when the temp is high enough to vaporize the fuel. the flash point is the lowest temp at which a liquid produces enough vapor to burn. - a solid such as wood burns only when exposed to heat hot enough to decompose into gaseous products (prolysis) - glowing combustion or smoldering is burning at the fuel -air interface, such as a cigarette, the embers of a wood fire, or a charcoal fire.
the cortex is the main body of the hair shaft
- its major forensic importance is the fact that it is embedded with the pigment granules that impart hair with color - the color, shape, and distribution of these granules provide the criminalist with important points of comparison among the hairs of different individuals
Other morphological features that could be important in comparing fibers are:
- lengthwise striations on the surface of the fiber - the presence of delustering particles that reduce shine - the cross-sectional shape of the fiber
oxidation background
- not all oxidation reactions proceed in a manner that one associates with a fire e.g. rusting - an oxidation reaction is associated with the concept of energy. energy is associated the ability of a system to do work. steam can turn a turbine to generate electrical energy. energy takes many forms e.g. heat and light - all oxidation reactions are examples in which more energy is liberated/freed than what is required to initiate the reaction. these are known as exothermic reactions.
the cuticle is the scale structure covering the exterior of the hair
- resistance to chemical decomposition & retention of structural features - the scale always points towards the tip of the hair - the scales are keratinized and flattened - the scale pattern is useful in species identification - 3 basic patterns (cornal, spinous, and imbricate)
Indicators of Arson
- some telltale signs of arson include evidence of separate and unconnected fires, the use of "streamers" to spread the fire from one area to another. - an irregularly shaped pattern on the floor resulting from the pouring of accelerant onto the surface.
bomb collection and analysis
- the entire bomb site must be systematically searched with great care given to recovering any trace of a detonating mechanism or any other item foreign to the explosion site. - objects located at or near the origin of the explosion must be collected for lab examination. often a crater is located at the origin and loose soil and other debris must be preserved from its interior for lab analysis.
other important features for comparing human hair:
- the presence/absence of a medulla - the distribution, shape, and color intensity of the pigment granules present in the cortex
morphology of hair
-Hair is an appendage of the skin that grows out of an organ known as the hair follicle -The length of a hair extends from its root or bulb embedded in the follicle, continues into a shaft, and terminates at a tip end. -It is the shaft, which is composed of three layers—the cuticle, cortex, and medulla —that is subjected to the most intense examination by the forensic scientist
for humans, the medulla is less than ____ the diameter of the hair shaft
1/3. while for animals it is generally one half greater
when properly collected and submitted to the lab accompanied by an adequate # of standard/reference ____ hair can provide strong corroborative evidence for placing an individual at a crime scene
25
a minimum collection of _______________________________________ should cover the range of characteristics present in pubic hair
25 dozen full-length pubic hairs
the collection of ______________________________ will normally ensure a representative sampling of head hair
25 full-length hairs from all areas of the scalp
medulla
A cellular column running through the center of the hair
black powder
a mixture of potassium or sodium nitrate, charcoal, and sulfer
secondary explosives
Relatively insensitive to heat, shock, or friction and will normally burn rather than detonate if ignited in small quantities in the open air
primary explosives
Ultra-sensitive to heat, shock, or friction and provide the major ingredients found in blasting caps or primers used to detonate other explosives
follicular tag
When pulled from the head, some translucent tissue surrounding the hair's shaft near the root may be found
Microspectrophotometer
a combination of a traditional light microscope and a spectrophotometer. it allows a forensic analyst to view an object under a microscope while simultaneously obtaining its visible of infrared absorption pattern
by comparing select gas chromatographic peaks recovered from fire-scene debris to known flammable liquids _____________________________
a forensic analyst may be able to identify the accelerant used to initiate the fire. the chromatographic pattern of the unknown is compared to patterns produced by known petroleum products.
Infrared spectrophotometry
a rapid and reliable method for identifying the generic class of fibers
microscopic hair examinations tend to be subjective and highly dependent on the skills and integrity of the analyst, because of this ___________________________________
a reported hair comparison must contain DNA information
root
along with other surrounding cells in the hair follicle provide the tools necessary to produce hair and continue its growth
the patterns of gasoline, as with many other accelerants, can easily be placed in a searchable library
an invaluable reference known as the ignitable liquids reference hydrocarbon collection (ILRC) is found on the int. at illrc.ucf.edu. - complex chromatographic patterns can be simplified by gas chromatography/mass spectometry
the probability of detecting DNA in hair roots is more likely for hair being examined in its ___________________________________ as opposed to its catagen (middle) or telogen (final) phases
anagen or early growth phase
three phases of hair growth
anagen, catagen, and telogen phases
the visible light microspectrophotometer is a convenient way for _________________________________________
analysts to compare the colors of fibers through spectral patterns
accelerant
any material used to start or sustain a fire
the most common igniter is a match
arsonists can construct many other types of devices to start a fire, including burning cigarettes, firearms, ammunition, a mechanical match-striker, electrical sparking devices, and a "molotov cocktail" - fortunately combustible liquids are rarely entirely consumed during a fire
arson investigator needs to begin exammining a fire scene for signs of arson ______________
as soon as the fire has been extinguished.
Collection of Fire Scene Evidence
at the suspect point of origin of a fire, ash and soot, along with porous materials which may contain excess accelerant, should be collected and stored in airtight containers such as new paint cans or wide-mouth glass jars, leaving an airspace to remove samples. Never use plastic containers to store fire scene evidence.
most widely used explosives in the low-explosive group
black powder and smokeless powder
mitochondrial dna is found in __________________
cellular material located outside of the nucleus and it is transmitted only from the mother to child
the gas chromatograph separates the hydrocarbon components and produces a ________________________________
chromatographic pattern characteristic of a particular petroleum product
a more detailed analysis of the fiber's dye composition can be obtained through a ______________________________________
chromatographic separation
if it is necessary to remove a fiber from an object, the investigator must use ________________________________
clean forceps, place it in a small sheet of paper, fold and label the paper, and place the paper packet inside another container
microscopic comparisons between questioned and standard/reference fibers are initially undertaken for ___________________________________
color and diameter characteristics, using a comparison microscope
recovered debris may also be thoroughly rinsed with organic solvents and analyzed by testing procedures that include __________________________
color spot tests, thin-layer chromatography, and gas chromatography/mass spectrometry
arson investigations often present ______________________
complex and difficult circumstances to investigate due to the fact that the perpetrator has thoroughly planned the act, is not present during the act, and the destruction is so extensive.
three mechanisms of heat transer
conduction, radiation, and convection
all positive microscopial hair comparisons must be ___________________________
confirmed by DNA analysis
smokeless powder
consists of nitrated cotton (nitrocellulose) or nitroglycerin and nitrocellulose
medulla may be __________________________
continuous, interrupted, fragmented, or absent
medullae also have different shapes __________________
depending on the species
natural fibers
derived in whole from animal or plant sources ex: wool, mohair, cashmere, furs, and cotton
debris and articles collected from _________________, are to be packaged in ___________ air tight containers
different areas, separate
a most useful physical property of fibers that many synthetic fibers exhibit ______________________________________ when viewed under a polarizing microscope. depending on the class of fiber, each polarized plane of light will have a characteristic index of refraction
double refraction or birefringence
typically, in the lab, debris collected at explosion scenes will be ______________________________
examined microscopically for unconsumed explosive particles
mitochondrial dna can be _________________________
extracted from the hair shaft
mass production of garments of fabric has limited the value of ___________________________________
fiber evidence
evidence of severe burning found on the floor (as opposed to the ceiling) of a structure is indicative as a
flammable liquid
the search of the fire scene must ________________
focus on finding the fire's origin, which may be most productive in any search for an accelerant or ignition device. - once located the point of origin should be protected. Notes, sketches, and photographs are taken. an examination should be performed.
often when hair is forcibly removed a ________________________ may be present
follicular tag. this has proven to be a rich source of nuclear DNA associated with hair
the most common request is to determine whether or not hair recovered at the crime scene compares to _______________________________
hair removed from the suspect
the investigator's task of looking for minute strands of fibers often becomes one of ______________________________
identifying and preserving potential "carriers" of fiber evidence
irregular patterns are common in post-flashover conditions
if the presence of ignitable liquids is suspected to have caused a fire pattern, supporting evidence from the lab for the presence of accelerant residues must confirm its existence
gas chromatograph
in the lab, the most sensitive and reliable instrument for detecting and characterizing flammable residues.
comparison microscope
indespinsible tool for comparing the morphological characteristics of hair
only the most unusual circumstances lead to _____________________
individual identification
the presence of the medulla varies from ___________________________________ and even among hairs of a given individual
individual to individual
By using DNA analysis on the follicular tag, the hair may be __________________
individualized
confirmatory identification tests may be performed on unexploded materials by
infrared spectrophotometry
trace evidence often corroborates other evidence in an ________________
investigation
if the examiner is presented with fabrics that can be exactly fitted together at their torn edges __________________________________
it is a virtual certainty that the fabrics were of common origin
the criminalist's function
limited to detecting and identifying relevant chemical materials collected at the scene and reconstructing and identifying igniter mechanisms. - the ultimate determination of the cause of a fire must be made by and investigator whose training and knowledge have been augmented by the experience of fire investigation
manufactured fibers
man made. - regenerated fibers are manufactured from natural raw materials and include rayon, acetate, and triacetate - synthetic fibers are produced solely from synthetic chemicals and include nylons, polyesters, and acrylics
Flashover factors
many factors can contribute to the deviation of a fire from normal behavior using burn patterns, such as depth of char, a V-shaped pattern, or low intense burn area, as indicators of a fire's origin can prove to be misleading when flashover has occurred.
Medulla index
measures the diameter of the medulla relative to the diameter of the hair shaft (expressed as a fraction)
two steps in the forensic examination of hair:
morphology and DNA
experience shows that _______________
most arsons are started with petroleum based accelerants. most common are gasoline and kerosene.
modus operandi
motive or pattern of operation
if most cases trace evidence can not be individualized, but through classification it_______________________
narrows the focus. the crime lab has developed instruments and techniques to compare and trace origins of trace evidence.
it is _______________________________________ to any single head or body through its morphology, however partial success for individualizing human hairs has been achieved by isolating and characterizing the DNA present in hair
not yet possible to individualize human hair
flashover
occurs when all the combustible fuels simultaneously ignite to engulf the entire structure - a fire that starts in one area of a structure could, through flashover, create the illusion of or more unrelated fires, a sign mistaken for arson.
when comparing strands of human hair, the criminalist is _________________________
particularly interested in matching the color, length, and diameter
Fibers can serve as evidence:
personal contact, hit and run, breaking and entering attempt
the vast majority of arsons are initiated by ________________________
petroleum distillates such as gasoline and kerosene.
hair is encountered as _____________ evidence in a wide variety of crimes
physical
it has been demonstrated that some explosives can diffuse through ________________
plastic and contaminate nearby containers
synthetic fibers are composed of __________________________ which are a large number of atoms arranged in repeating units known as monomers
polymers, or macromolecules
Mitochondrial dna has a high frequency of occurence in a _______________
population and thus cannot be used to individualize a hair, but it does provide valuable corroboration of a morphological hair comparison
secondary explosives must be detonated by a ____________________
primary explosive
Hair and DNA
recent major breakthroughs in DNA profiling have extended this technology to be individualization of human hair.
particularly important in animal hair identification
scale structure, medullary index, and medullary shape
Ion Mobility Spectrometer
screening object for the presence of explosive residues
all materials collected for the examination by the lab must be placed in ____________________
sealed airtight containers and labeled with all pertinent information
the molecules that compose a manufactured fiber __________________________
selectively absorb infrared light to form a characteristic pattern
relevant articles of clothing should be packaged carefully in __________________
separate paper bags
detonation
speed of decomposition. extremely rapid producing a supersonic shock wave creating a blast effect with an outward rush of gases at speeds as high as 7,000 miles per hour. In recent years, nitroglycerin-based dynamite has all but disappeared from the industrial explosive market and has been replaced by ammonium nitrate-based explosives
explosives
substances that undergo a rapid oxidation reaction with the production of large quantities of gases. This sudden buildup of gas pressure that constitutes the nature of an explosion. the speed at which explosives decompose permits their classification as high or low explosives.
hair samples are also collected from the victims of ________________________
suspicious deaths during an autopsy
the quality of the fiber evidence depends on ____________________
the ability of the criminalist to identify the origin of the fiber or at least be able to narrow the possibilities to a limited number of sources
Polymer
the basic chemical substance of all synthetic fibers
Oxidation
the combination of oxygen with other substances to produce new substances. fire is a type.
ultimate (fiber evidence) value depends on ________________________
the criminalist's ability
heat of combustion
the heat involved when a substance burns. once combustion starts enough energy in the form and light (flame) is liberated, a portion of which is used to sustain the fire. Fire is a chain reaction
conduction
the movement of heat through a solid object. poor conductors are called insulators. during a fire heat may transport through metals, such as nails, bolts, and fasteners to a location far from the initial heat source creating a new fire location.
normally a fire has a tendency to move in an upward direction and thus ____________________________
the probable origin will most likely be the lowest point showing the most intense characteristics of burning
low explosives are confined to a container like a pipe
the speed of decomposition is called deflagration causing the walls of the container to fragment and fly outward in all directions.
Convection
the transfer of heat energy by the movement of molecules within a liquid or gas. in a structural fire, hot gases move to the upper portion of the structure causing surfaces to pyrolyze and burst into a fire.
high explosives
this group comprises the majority of commercial and military blasting, such as dynamite, TNT, PETN, and RDX
Ignition Temperature
to start a fire, the minimum temp needed to spontaneously ignite a fuel must be reached. Example: Gas: 536 degrees Fahrenheit or Kerosene: 410 degrees Fahrenheit.
Radiation
transfer of heat energy by electromagnetic radiation. a surface exposed to the heat of a fire may burst into flames when the surface reaches the ignition temp.
accelerant identification
typically a forensic analyst compares the pattern generated by the sample to chromatographs from accelerant standards obtained under the same conditions.
vapor detector (sniffer) or a trained canine
used to help trace flammable liquid residue - collection of all material suspected of containing volatile liquids must be accompanied by a thorough sampling of similar but uncontaminated control specimens from another area of the fire scene, called a substrate control.
