CJ 110 EXAM 1Identify the evidence and known samples in an example.

Identify the evidence and known samples in an example.

The evidence (unknown) sample is material collected from a crime scene or other source whose origin is being determined. A known sample is a reference sample obtained from a known person, object, or source for comparison.

Ask the correct question when a trait of evidence and a known sample matches.

“Is this characteristic consistent with the known sample?” A match supports that the evidence and known sample could have the same source, but the significance depends on the type of evidence and the examination.

Ask the correct question when a trait of evidence and a known sample does not match.

“Is this characteristic inconsistent with the known sample?” If a reliable, discriminating characteristic cannot be explained by variation, the known sample can be excluded as the source.

Select the correct conclusion given a description of evidence analysis.

inclusion/consistent, exclusion/inconsistent, or an appropriate inconclusive/indeterminate conclusion. Do not claim more certainty than the method supports.

Explain why forensic scientists should not use the terms “likely” or “not likely”.

Those phrases are vague and can be interpreted as subjective probabilities. Forensic conclusions should use defined terminology and clearly communicate the limits of the evidence and method.

Explain why forensic scientists should not testify about guilt or innocence.

Forensic scientists evaluate evidence, not the ultimate legal question. Guilt or innocence is determined by the court or fact-finder after considering all evidence.

List the five different career categories for forensic science related professions.

▪ Investigation

▪ Laboratory Work

▪ Crime Scene Work

▪ Performing Autopsies

▪ Looking at Bones and Bugs

Describe the job duties for each career category.

Laboratory: analyze physical evidence such as DNA, drugs, trace materials, firearms, and questioned documents.

Crime scene: document, collect, preserve, and interpret evidence. Medicine/health: perform examinations and determine medical causes or findings.

Behavioral: apply psychology to legally relevant questions. Support/investigative: provide specialized technical, identification, records, or investigative services.

Identify the major and degree level required for each career category.

Laboratory scientists commonly need a bachelor's degree or higher in a natural science such as chemistry, biology, forensic science, or a closely related field. Specialized medical careers require professional degrees and licensure. Behavioral careers commonly require psychology or a related degree, with advanced degrees for many roles. Crime-scene and support roles vary by agency and position.

Describe the work a forensic scientist does inside and outside the laboratory.

Inside the lab, a forensic scientist examines evidence, performs validated tests, documents results, interprets findings, and maintains quality-control records. Outside the lab, the scientist may attend scenes, consult with investigators, review evidence, explain methods, write reports, and testify in court.

Describe the job levels for a forensic scientist and the duties for each level.

Typical levels progress from entry/junior work under supervision, to experienced/qualified analyst who independently performs examinations, to senior/technical leader who handles complex cases and reviews work, and potentially supervisory/managerial roles overseeing personnel, quality, training, and operations.

List the agencies where a forensic scientist could work.

State Agencies

▪ State Police

▪ State Bureau of Investigation

▪ County or City Crime Labs

Federal Agencies. FBI, DEA, ATF, Armed

Forces, Secret Service, USPS

List the labs where a forensic scientist could work.

Private Forensic Science Labs

▪ Private DNA Labs

▪ Paternity Labs

▪ Drug Analysis

Non Forensic Laboratories

▪ Analytical Labs

▪ Research Labs

Identify primary and secondary crime scenes.

Primary Crime Scene. where the original crime occurred

Secondary Crime Scene. subsequent crime scenes

Describe the Locard Exchange Principle.

when two objects come into contact with one another, an exchange of matter takes place.

List information that evidence at crime scene can provide to investigators.

▪ Linking people, objects, crime scene

▪ Identification of unknown substances

▪ Proving which crime was committed

▪ Linking multiple crimes together

▪ Proving witness/suspect statements

▪ Providing investigative leads

List the order of events when processing a crime scene.

1. First Officer on the Scene

2. Securing the Crime Scene

3. Crime Scene Walk-Through

4. Crime Scene Documentation

5. Searching the Crime Scene

6. Collection of Physical Evidence

Describe the duties of the first officer(s) at the scene.

▪ Safety of the first responders and victim is the primary concern. Assist the victim even if scene is disturbed.

▪ Search for and arrest suspect

▪ Detain and separate witnesses

▪ Protect the crime scene (barrier tape)

▪ Note any changes made to the scene

Describe the crime scene survey.

After the scene is secure, the investigator and first responder do a survey or “walk-through”

▪ Prepare an initial reconstruction

▪ Note any temporary evidence

▪ Note entry/exits that require attention

▪ Access scene for personnel, precautions, and equipment needed

Explain how officers videotape and photograph the crime scene.

▪ Introduce with case #, date, location

▪ Begin with surroundings (include entrance/exits)

▪ Tape Evidence (wide angle, close-up)

DO NOT:

▪ Narrate the video or discuss contents

▪ Edit original video

Explain how officers photograph the crime scene.

▪ Take examination quality photographs or digital images (used by experts to interpret evidence)

▪ Every photo should be recorded in a log

▪ Take with and without a scale

Describe how evidence is collected, labeled, and handled at the crime scene.

▪ One individual designated as evidence collector

▪ Temporary, fragile, or easily lost

evidence should be collected first

▪ Evidence placed in primary and secondary containers

▪ Liquid or volatile evidence placed in airtight containers

▪ Biological evidence placed in non-airtight container and allowed to dry

▪ Each item packaged separately

Identify the types of blood cells in blood, including those that contain DNA.

▪ Red Blood Cells do NOT contain DNA

▪ White Blood Cells DO contain DNA in the nucleus

Name the protein that carries oxygen in the blood.

hemoglobin

Describe the presumptive test reaction used to test for blood.

Positive result means the questioned stain is possibly blood.

Negative result means the questioned stain is probably not blood.

Name the protein in the blood that catalyzes the presumptive test reactions.

hemoglobin

Name 2 presumptive tests for blood.

▪ Tetramethylbenzidine (TMB). Also found in hemastix.

▪ Phenolphthalein. Also called Kastle- Meyer test.

Describe the methods for presumptive tests.

▪ Moisten cotton swab

▪ Rub swab on stain

▪ Add drop of chromogen

▪ Add drop of hydrogen peroxide

Name the false positives for presumptive blood tests.

▪ Chemical Oxidants

▪ Plant materials

Describe the appearance of blood, including the appearance under alternative light.

Fresh liquid blood is red and becomes darker as it dries. Under alternative light, blood may appear dark or may show enhanced contrast depending on the wavelength and surface; it does not inherently fluoresce like some other biological stains.

Describe a chemiluminescence reaction.

light is emitted as a product of the chemical reaction

Name the chemiluminescent reagent used to search for blood.

Luminol is a commonly used chemiluminescent reagent for locating possible blood traces.

Describe the method for using luminol.

▪ Reaction is similar to color test

▪ Luminol is combined with oxidant and sprayed over area thought to contain blood

▪ Emits a blue-white to yellow green glow

Name the cells found in semen.

▪ Cells

▪ Enzymes

▪ Other organic and inorganic materials

Describe the ways sperm count may be lower in some males.

due to disease, genetics, drugs/alcohol, or vasectomy

Describe how semen appears under alternate light.

Look for fluorescence

Name the one presumptive and two confirmatory tests for semen.

▪ Test for seminal acid phosphatase (SAP)

▪ Brentamine Fast Blue Test

▪ AP Spot Test

Describe the method and color change for the AP spot test.

▪ Swab moistened with water

▪ Swab is rubbed over semen stain

▪ Reagent containing both substrate and chromogen is dropped on swab

▪ Positive reaction is a purple color

List the false positives for the AP spot test.

▪ Other materials with low AP levels (urine, vaginal secretions, perspiration) may produce weak reactions.

▪ Old semen stains may also produce a weak reaction.

▪ Fresh semen stains will produce an immediate, strong color change reaction.

Describe the method for the Christmas tree stain.

▪ Collect portion of stain on moist swab or take small cutting of stain.

▪ Tease apart fibers in a drop of water on a microscope slide. Dry slide.

▪ Stain with red dye and rinse. Stain with green dye and rinse.

Describe the method for the PSA tests.

▪ Swab or cutting agitated in water

▪ Drop of this solution added to test well

▪ Liquid moves through result well

▪ Antibody is already bound to membrane

▪ Visible test line (T) means PSA is present

▪ Control line (C) shows test was done properly.

Describe the enzyme detected in saliva tests.

amylase

Name the presumptive test for saliva.

▪ Starch-iodine test

▪ Phadebas Reagent

Describe the Phadebas methods used to search for saliva and test for saliva.

▪ Phadebas paper contains phadebas reagent (dye linked to starch) on one side of paper

▪ Phadebas paper (blue side down) is placed on the area to be searched. Paper is sprayed with water and pressed against area.

▪ Amylase in saliva breaks down starch, releasing blue dye through paper.

List the false positives for the Phadebas test.

Since amylase is present in other body fluids, other fluids may cause a false positive. low levels of saliva may not be detected.

Explain why saliva stains are not usually tested before moving on to DNA testing.

▪ Since the phadebas test uses up some sample, the test may not be done before DNA testing.

▪ In some samples, saliva presence can be inferred: envelopes, drink containers, bite marks.

Know what the acronym DNA stands for.

deoxyribonucleic acid

Describe what DNA does for a living thing.

DNA stores genetic information and provides instructions used by cells to make proteins and regulate biological processes. It is passed from parents to offspring.

Describe the molecular appearance of DNA.

DNA has a double-helix structure, often described as a twisted ladder.

Name the building block of DNA.

nucleotide

Describe where the bases are located in DNA.

The nitrogenous bases project inward from the sugar-phosphate backbones and pair with bases on the opposite strand.

Name the 4 bases (letters) of DNA.

Adenine (A), thymine (T), cytosine (C), and guanine (G).

Describe how the bases pair with one another.

The bases pair up to form the rungs of the ladder.

Memorize the number of base pairs in one copy of DNA.

there are three billion base pairs (letters) in one copy of DNA within each cell.

Memorize the percentage of the DNA sequence that is the same among humans.

Among humans, 99.8% of the 3 billion bases in the DNA sequence are the same

Name where DNA is located in a cell, including the location of chromosomes.

DNA in the nucleus is packaged into chromosomes.

Describe how DNA is organized in cells.

 46 chromosomes in each cell, or 23 pairs

 For each chromosome, one comes from mother, and one from father

Describe where cells are located in different parts of the body.

 Blood, Semen, Saliva

 Tissue, Bone, Teeth, Hair, Maggot Crops

Describe the 3 ways DNA can be different among individuals.

 DNA is a sequence of 4 possible letters

 Of the 3 billion letters, 99.8% of the sequence in all humans is identical.

 There are several ways the sequence can be different.

Identify which difference is used by forensic scientists to identify an individual.

1. One of the base pairs (letters) can be different.

2. Base pairs (letters) can be added or removed.

3. Regions of DNA can be repeated a different number of time

Describe unknown and known samples used for DNA analysis.

Types of Unknown Samples:

 Blood stain, Semen stains, Saliva residue

 Hair, Tissue, Bones, Teeth, Sweat

Types of Known Samples:

 Blood or buccal swabs from suspect or victim or other known person

Describe how DNA evidence should be packaged.

 Package each item individually.

 Put evidence into paper bags, not plastic.

 Moisture degrades DNA; air dry samples.

 Keep samples at room temperature and out of sun.

Name and describe the forensic markers that are used in the FBI database.

The FBI's national DNA database system uses STR markers. CODIS profiles use a standardized set of STR loci; the current core set is 20 loci. These markers are highly variable and are used to compare DNA profiles.

Describe locus and allele. Identify the locus and allele in a given DNA profile.

A locus is a specific location on a chromosome. An allele is a particular version of the DNA sequence at that locus. In an STR profile, allele numbers generally indicate the number of repeat units detected at a locus. For example, a profile showing 12,14 at a locus has alleles 12 and 14.

Explain why 13 loci are used in the FBI database.

Using multiple independent loci greatly increases the power to distinguish unrelated individuals.

Describe what happens during the extraction and amplification steps.

Extraction - separates DNA from sample

Amplification or PCR - amplifies small portions of DNA (STR regions)

Describe how a forensic scientist would present a matching profile in court.

The scientist should explain the methods, quality controls, profile comparison, statistical significance, and limitations. Rather than simply saying “this is the person's DNA,” the scientist should state the scientifically supported conclusion and provide an appropriate statistical measure, such as a random match probability or likelihood ratio when applicable.

Identify when a non-matching profile would give an analyst a “definitely no” conclusion.

An exclusion is appropriate when reliable differences are found at one or more genetic markers that cannot be explained by accepted factors such as a mixture, mutation, or analytical artifact. The reference person is then excluded as a contributor/source for that profile.

Memorize the approximate number of base pairs in the mtDNA genome and the number of base pairs that are analyzed.

he mitochondrial genome is about 16,569 base pairs. Traditional forensic mtDNA sequencing focuses on variable regions, especially the control region; the exact number analyzed depends on the method and sequencing strategy.

Describe how mtDNA analysis may be more useful than STR analysis.

mtDNA can be especially useful when nuclear DNA is highly degraded or when there is little nuclear DNA. Because mitochondria occur in many copies per cell and mtDNA is maternally inherited, it can also help with certain missing-person or maternal-line comparisons

Describe the limitation of using mtDNA.

mtDNA is not as individually discriminating as a full nuclear STR profile because people sharing a maternal lineage can have the same or very similar mtDNA. It therefore generally cannot distinguish all maternal relatives from one another

Describe the difference between a smooth barrel and rifled barrel.

Smooth Barrel. Hollow tube

Rifled Barrel. Barrel of gun can be rifled to put spin on bullet; increases accuracy

Name the terms for the raised and lowered areas of a rifled barrel.

The raised areas are called lands; the lowered channels are called grooves

Describe how the manufacturing process causes differences to the inside of a barrel.

Manufacturing processes leave microscopic imperfections and toolmarks on the barrel's interior. These can contribute to individual characteristics that may be transferred to bullets fired through the barrel.

Describe the 4 categories of guns, including which type of projectile each type fires.

Describe the difference between a bullet and shot pellets.

A bullet is generally a single projectile fired from a rifled firearm. Shot pellets are multiple small spherical projectiles commonly fired together from a shotgun shell.

Describe the function of a primer in an ammo cartridge.

▪ When hit with hammer, primer creates a small explosion

▪ This explosion lights propellant creating a large explosion (propels bullet)

Describe the propellant used in ammunition.

▪ Modern propellants are smokeless powders composed of nitrocellulose.

▪ Some propellants contain nitrocellulos and nitroglycerin .

Describe how bullets should be collected at the crime scene.

▪ Either collect the item containing embedded bullet or…

▪ Use rubber coated forceps to remove bullet

List class characteristics of casings.

▪ Caliber (size)

▪ Firing pin location, size, and shape

▪ Extractor and ejector sizes

▪ Relative location of extractor and ejector

Describe the individual characteristics of bullets.

▪ Caliber (size)

▪ # of lands and grooves

▪ Width of lands and grooves

▪ Direction and degree of rifling twist

Name the tiny scratches on fired bullets.

striations

Describe the conclusions of analysis.

▪ If class characteristics and striations match, can say the bullet was fired by the suspect gun.

▪ If class characteristics (and striations) do not match, the suspect gun can be excluded.

▪ If class characteristics match but striations do not, the results may be inconclusive.

Describe where GSR is located after firing.

▪ Long distance. no GSR on the victim

▪ Close-range. GSR on victim is spread out

▪ Near-contact. GSR on victim is concentrated circle

▪ Contact shot. “Blown out” entrance wound

Describe how GSR is collected and tested from a suspect's hand.

Hand/glove/paw is swabbed to collect GSR.

Swab is analyzed using the following:

▪ Elements barium and antimony are found in

high levels.

▪ Use powerful microscopy (SEM)

▪ Use chemical tests (color change reactions)

List the elements found in GSR.

mixture of materials that originate from the firing of a gun.

Describe how GSR on a victim can be used to estimate the range of fire.

can be estimated by looking at gunshot residue patterns