Download CHAPTER 3 and 4 (Mostly 4)

CHAPTER 3 and 4 (Mostly 4)
Crime-Scene Reconstruction
• What is reconstruction exactly?
– Definition: the method used to support a likely sequence of events at
a crime scene by observing and evaluating physical evidence and
statements made by those involved with the incident.
• What is the purpose of crime-scene reconstruction?
– This helps us to answer questions such as: Was more than one person
involved? How was the victim killed? Were actions taken to cover up
what actually took place?
• Who works together to reconstruct?
– Experienced law enforcement personnel, medical examiners, and
criminalists.
• What is the foundation of reconstruction?
– Answer: the COLLECTION and DOCUMENTATION of physical evidence.
Examples of Crime-Scene
Reconstruction
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Determining whether a body was moved after death
Determining whether a victim was clothed after death
Analyzing bullet trajectory
Analyzing blood spatter
Determining direction from which projectiles penetrated glass
objects
Estimating the distance of a shooter from a target
Locating primer residue on suspects
“What is a windmill? What does it do?” Hahaha So funny!
Now that we’re being random…I can’t believe I THOUGHT I
recorded Gossipgirl, but found out to my awful dismay that I indeed
did NOT, even though I distinctly remember pressing the RED
“Record” button! Oh wow, I am behind again on the show…No one
can talk about it yet, okay?
Figure 3-8
• Take a look at this figure on p. 94 of the text.
How will the position of a shooter who fired a
bullet through a window be determined?
• Bonus question: Who is the shooter? Well if
Sarina Vanderwoodsen is capable of killing
someone once, she is definitely capable of it
twice…dun dun dun (stated in a dangerous
tone)!
Properties of Matter/Glass Analysis
• Properties of Matter:
– Physical: weight, volume (L’oreal might have good
products…), color, boiling point, melting point;
– On a positive note: I did get to see One Tree Hill and
Privileged, and they were both good!
– Chemical (describes behavior of a substance when it
combines/reacts with another substance): i.e. wood
burning; wood combines with oxygen and forms NEW
substance;
• In the crime lab, a common analysis that is an example of the use
of chemical properties is when testing for the presence of heroin
by reacting the suspect specimen with Marquis reagent, a
chemical that would turn purple in presence of heroin.
Properties of Matter/Glass Analysis
• What you should know about light:
– It can make or break your school pictures. It’s okay, no one really looks at the
yearbook anyway, right?
– Dispersion=the separation of light into its component wavelengths
– Refraction=the bending of a light wave caused by a change in its velocity
– Visible light=colored light ranging from red to violet in the electromagnetic
spectrum
– Electromagnetic Spectrum=entire range of radiation energy from the most
energetic cosmic rays to the least energetic radio waves
– Look at figure 4-3 and 4-4
– Laser=Light Amplification by Stimulated Emission of Radiation AKA: light that
has all its waves pulsating in unison.
– Photon= a discrete PARTICLE of electromagnetic radiation
– KEY IDEA: forensic scientists characterize different chemical substances by the
TYPE and QUANTITY of light they absorb
– Obama or McCain? Obama or McCain? Wait, am I even registered to vote? Yes
I am!!! Good.
Physical Properties of Matter
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Temperature
Weight and Mass
Density (mass divided by volume)
Refractive Index- (def.) the ratio of the speed
of light in a vacuum to its speed in a given
medium
• Buehler…Buehler…Buehler (hope I spelled it
right!)
Glass Analysis
• How can we use glass to help us in the crime scene
analysis?
– Broken glass from a window may get caught in the suspect’s
shoes or clothing/garments.
– Particles of a headlight glass (i.e. in a hit and run incident) can
help identify/confirm the identity of the suspect’s vehicle
– Basically it is one more source of evidence!
– What the Scarecrow in the Wizard of Oz would say at the voting
booth: “If only I had a brain…If only I had a brain” Too bad, we
could’ve used his vote, since so many people who DO have a
brain don’t vote anyway! Actually we could use his vote also for
the reason that so many people who DO vote don’t seem to
have a brain either…yeah, so we could use his vote afterall…
Glass Analysis
• Composition of Glass: hard, brittle, amorphous
(without definite shape); composed of sand and other
metal oxides.
• Tempered Glass: glass that is strengthened through the
process of rapid heating and then cooling of the glass
surfaces.
• Laminated Glass: two sheet of ordinary glass that are
bonded together with a plastic film
Q: What is the result of the strength of tempered glass?
A: It will usually hold together without splintering (Fig. 412 of p. 132 in text)
Specific Ways Glass is Analyzed
• Matching the broken pieces in a sort of puzzle.
– This is not usually the best means of comparison, since most glass
evidence is too fragmented or too small to permit this type of
comparison.
• The trace elements present in glass may be more useful. These
provide a source of more distinct and more measurable
characteristics.
• Density and Refractive Index are one of the best ways to
characterize glass particles
• Subliminal Message: Ms. Hashempour is the best. She is so
magnificent. She is the best teacher I EVER had…I will buy her furs
and diamonds…Oops, that subliminal message was not so
subliminal. Oh well, now you know what to buy me for my birthday!
Measuring and Comparing Density
• How is that when you want to say that someone is dumb you say
that they are “dense” but that the scientific meaning of “dense”
would mean that there is a lot of matter or substance? Doesn’t
someone who is dumb lack matter or substance in his/her brain?
Just food for thought…
• Flotation- What you did in the pool when you were 6 years old (no,
not peeing in the pool, although you probably did that too! How
could you?!) Okay, the real definition: the process of immersing a
standard/reference glass particle in a liquid; the liquid is usually a
mixture of bromoform and bromobenzene. When other pieces of
glass are added to this solution for comparison, then the density of
the glass can be determined relative to the newly added pieces of
glass. Note: of course the added pieces of glass must be the same
size and same shape. These must be the control factors.
Refractive Indexxx
Refract that Bizness ;)
• Once the density of glass is determined then refractive index is the next
characteristic that refines your identification. This means that density
determination is sort of a stepping stone for the next step of the
identification process.
• An immersion fluid (the fluid the glass is immersed in) will help determine
the refractive index, since the glass will refract light in a certain way in that
particular medium. Understand that the basis of refractive index is: that
glass refracts light differently in different mediums. It will refract that bizz!
Just like you act differently around your different friends, glass too will act
differently when it is “associated with” its different friends (mediums)!
• Also know that this process can be specified even more by adjusting the
temperature of the immersion fluid. Remember: in Science, temperature
is a KEY variable that scientist change! Tempo tempo temperature…Tempo
tempo temperature… Can I get a beat? Why am I so weird? I might make
that into a multiple choice question on the next exam…Actually no I won’t
because I’m scared to know what you guys will answer…!
Okay okay…but…
• What if density and refractive index don’t
work to help us? What if two pieces of glass
exhibit comparable densities and comparable
refractive indices? How can we know if they
did, in actuality, come from the same source?
Hmmm. Let’s take a moment to think about
it… “Ooh oooh I have the answer (Ms. H
impatiently raises her hand)!”
Answer:
• The FBI Laboratory has collected density and refractive
indices values from glass submitted to it for
examination, and thus what has been created is a data
bank that correlates these values to their frequency of
occurrence in the glass population of the United States.
Wow they’re good!
• By the way: Does anyone else think that the phrase
“glass population” sounds weird? I mean, it sounds like
the glass is a living, breathing population of beings with
a mind and life of their own, holding a place in
society…Okay maybe I over-thought that one…anyway.
Glass Fractures
• Radial – crack in glass the goes outward like
the spoke of wheel from the point at which
the glass was struck.
• Concentric- crack in glass that forms rough
circle around point of impact.
• Look to figure 4-17 (p.139) to see an example
of both of these within one picture.
• Figure 4-19: Shows how FIRST radial cracks are
formed and THEN concentric cracks form.
Collecting and Preserving Glass
• If the examiner is collecting glass, he/she must make
sure and collect ALL pieces of glass and thus do a
thorough job of collection, especially if aiming to piece
them together in the “puzzle” method—when glass
pieces are matched together to recreate the original
composition of the whole glass item.
• Examiner distinguishes several items of interest before
submitting evidence: i.e. determining direction of
impact onto the glass, determining which side is an
interior surface versus exterior surface. Note:
Determining whether a surface is an exterior surface
(as opposed to an interior one)can be determined
through presence of dirt, grease, or putty.