Forensic Science: Chapter 8

The Microscope

characteristics of a virtual image (3)

-image that cannot be seen directly

-can only be seen by looking through a lens

-formed by the eyepiece of the microscope

characteristics of a real image (2)

-an image that can be seen directly with the naked eye

-produced through the objective lens on the scope

What is the compound light microscope used to see?

-to determine the species from sperm, blood, hair, etc

What are the two lenses of the compound light microscope?

-objective

-ocular (eyepiece)

objective lens

the lens closest to specimen

ocular lens

the lens closest to the eyes

What are the parts of the mechanical system? (7)

-base

-arm

-stage

-stage clips (clamps)

-body tube

-coarse adjustment knob

-fine adjustment knob

base

the stand for support

arm

acts as a handle

stage

the horizontal platform to place specimens

stage clips (clamps)

holds slides and supports the specimen

body tube

cylindrical hollow tube light passes through objective to eyepiece

coarse adjustment knob

focuses microscope on specimen and raises/lowers the body tube

fine adjustment knob

finer focus and adjusts the height in smaller increments

What are the parts of the optical system? (4)

-illuminator

-condenser

-objective lens

-ocular lens (eyepiece)

illuminator

artificial light supplied by light source

What illumination comes from the illuminator? (2)

-transmitted illumination

-vertical illumination

characteristics of transmitted illumination (2)

-for transparent specimens

-light is directed up from illuminator built into base

characteristics of vertical (reflected) illumination (2)

-for opaque specimens

-collects light rays from the base illuminator and focuses onto specimen

parfocal

the image is focused with 1 objective and another objective can be rotated into place and field will remain in focus

What are the two types of eye lenses?

-monocular

-binocular

monocular

1 eyepiece

bionocular

2 eyepieces

magnification

the ability of the microscope to make the image larger

resolution

the ability to form images into fine detail

field of view

the size of the specimen area

depth of focus

thickness of specimen that is entirely in focus under a scope

What is the relationships between magnification and depth of focus?

-as magnification increases, depth of focus decreases

comparison microscope

2 compound microscopes combined into 1 unit for a side-by-side comparison of 2 specimens

What is a comparison microscope used for?

-bullet comparison

What is vertical illumination for comparison microscopes used for?

-bullets

-cartridges

What is transmitted illumination for comparison microscopes used for?

-hairs

-fibers

What are the advantages of a stereoscopic microscope? (5)

-large working distance

-distinctive 3-D image

-create right-side-up image

-wide field of view and great depth of focus

-view live organisms

What are stereoscopic microscopes used to locate?

-trace evidence

What microscope is the most commonly used in the crime lab?

-stereoscopic microscope

plane polarized light

confined to a single plane vibration

What does the polarizing microscope examine?

-examines birefringence of minerals in the soil

microspectrophotometer

a microscope that uses selective absorption spectra of light and links a light microscope to a computerized spectrophotometer

What is the microspectrophotometer used to obtain?

-absorption spectrum

scanning electron microscope

directs beams of electrons onto specimen to form an image

What are the advantages of an SEM? (3)

-high magnification power

-high resolution

-great depth of focus

What are the SEM forensic applications? (6)

-gunshot residue

-firearms ID and bullet comparison

-examination and identification of paint particles, fibers, and gemstones

-filament bulbs in traffic accidents

-counterfeit money/notes

-trace comparison

What is the procedure to determine if someone recently fired a gun?

1. adhere tape lift of suspects’ hands

2. place tape in the SEM

3. particles on the tape are analyzed by an X-ray

4. the particles are displayed by their energy

   1. examiner can detect elements found in bullet primers

What elements are found in bullet primers? (3)

-barium

-antimony

-lead

forensic microscopy

examination of microscopic evidence as it relates to the law

forensic palynology

collection and examination of pollen and spores connected with a crime scene

What are the uses for the analysis of spores and pollen? (13)

-link suspect/objects to crime scene/victim

-prove/disprove suspect’s alibi

-include/exclude suspects

-track previous whereabouts of item/suspect

-indicate geographical origin of item

-help locate human remains/concealed burial sites

-establish season/time of death

-locate sources of illegal drugs

-imprison terrorists

-solve cases involving illegal poaching

-build profile of a suspect

-point the investigation in the right direction

-determine the season in which the crime occurred

Sweden 1959 Case

-first case using forensic palynology

-the crime wasn’t solved

-young woman was murdered

Austria 1959 Case

-sight seeing boat in Vienna

-evidence was the pollen on boots

-man killed his business partner

Illinois 1980 Case

-kidnapped and murdered a farmer

-stole money

-robs a liquor store and gets caught

-corn maze pollen found on suspect’s shoulders

Texas 1995 Case

-found a torso

-victim was stabbed 21 times

-collected pollen from marijuana and from Kansas

-believed to be murdered by the Mexican drug cartel

New York City Case

-collected cocaine

-tries to find out how and where the cocaine came from

-cocaine is from South America/Bolivia, then shipped to Canada, and then to New York City

How are you able to tell female vs. male by barr bodies?

-females have a barr body and males do not

What can you get from karyotypes? (2)

-gender

-missing or extra chromosomes

What additional steps can be taken to identify skeletal remains?

-compare dental records to teeth

-clothing containing hair, fibers, etc

-DNA from dental pulp

-jewelry, tattoos, piercings (identifying marks)

Why was a forensic documenter called in on the Lindbergh case?

-he looked at handwriting from the suspect to the ransom note

-the “y” had a tail and the “o” was not closed

-suspect was German

-tool marks on the ladder matched the suspect’s tools

-the wood from the ladder was the same wood missing from the suspect’s attic

-had the gold tickets

-had the name and phone number of the intermediator in his closet

Baby Doe Case

-baby found in Boston along the shore

-hair and clothing was tested

-cedar pollen was found and matched a nearby area

-the baby’s name was Bella Bond

What is the difference between bird blood and human blood?

-human red blood cells do not contain nuclei but bird cells do

What is the difference between bull and human sperm?

-bull sperm is large and blunt, human sperm is oval and small

What does SEM tell us about pollen?

-the species of pollen

What does the compound microscope tell us about hair, blood, sperm, etc?

-the species