Forensic Science unit 1 exam

september 26th, 2026. this includes notes from reading chapters, quiz questions, and notes from lecture

Locard’s Principle:

Locard was the first to realize that there is Trace evidence at crime scenes, and that when perpetrators come into contact with the scene, they will leave something of themselves and take away something from the scene.

locards exchange principle applies to ________ evidence.

biological, physical, and trace.

• also known as transfer evidence

Deductive reasoning:

also known as Inference, it uses logical steps to draw a specific conclusion from know facts, physical clues, and scientific principles

inductive reasoning:

its how to interpret evidence or a statement by gathering clues, and observations to build a probable conclusion about how a crime happened or who committed it.

inclusive evidence:

it is a category of evidence, and is a physical or biological material that consists between crime scene evidence and a known sample from a person of interest. it INCLUDES the person as a possible source but does not prove guilty, only shows association

circumstantial evidence:

it is a category of evidence, and suggests a fact through clues. many cases are built on circumstantial evidence. it is INDIRECT

indeterminate evidence:

category of evidence, and is information that is inconclusive which cannot prove a hypothesis. you cannot make a positive identification of a suspect.

a DNA test of blood at a homicide scene is found to match suspect A who lives at the residence. in terms of placing suspect A at the scene, this evidence is ______.

circumstantial

A firearm is located at the scene of a murder. the firearm is identified as the murder weapon and a fingerprint found on the firearm does not match suspect A. in terms of suspect A, this evidence is exculpatory. True or False?

True

exculpatory evidence:

a category of evidence, and indicates individuals in a crime of being innocent, such as someone who has a confirmed alibi (video footage of individual at time of crime)

forensic scientists:

uses scientific methods and laboratory techniques to analyze physical evidence. scientific includes biology, physics (blood spatter, projectile), geology, anthropology, toxicology (bodily fluids), entomology.

criminologist:

a social scientist who studies nature, pattern, extent, cause, and control of criminal behavior

criminalist:

a forensic science professional who collects, identifies, and analyzes physical evidence and contributes information of a case.

primary crime scene:

it is the original, main location where a criminal act took place.

secondary crime scene:

the other location that was related to the crime, evidence was moved or disposed of, but not the original crime scene.

class characteristics:

traits or measurable features that place an item or person into a specific group, but does not pinpoint a single individual item or person. such as blood type narrows down a group of people who share the same type, or brand of shoes narrows it into a group.

individual characteristics:

unique or random features on an object or person that can link evidence to a single, specific source with a high degree of certainty. such as DNA, fingerprints.

cause of death:

it is the disease or injury that initiated the lethal chain of events.

mechanism of death:

a biochemical or physiologic abnormality produced by the cause of death. this is often done by the medical examiner and coroners.

manner of death:

it describes the circumstances/classification of the death which could be NASH.

true or false, an example of cause of death is homicide.

False

true or false, an example of mechanism of death is strangulation.

false

true or false, an example of manner of death is lack of oxygen to the brain.

false

rigor mortis:

the stiffening of the muscles which is caused from the chemical reaction of glycogen, and occurs 4 hours after death and lasts up to 24-36 hours. heat accelerates process.

algor mortis:

it is the cooling of the body, and drops 1.5 C per hour. this is the most accurate way to determine time of death. it begins 30 minutes-1 hour after death.

livor mortis:

it is the discoloration of the body(lividity) caused by the settling of red blood cells (blood settles at lowest part of the body) and creates a red/purplish color. this occurs 1 hour after death, and lasts up to 36 hours.

the general purpose of a death investigation is to determine the ____ of death.

all of the above (cause, mechanism, and manner)

what can livor mortis indicate? and how can we tell?

it might indicate whether a body has been moved after death.

blanching:

when no color goes where direct pressure has been on. for example, someone died laying on their back, so when examined they have white splotches on the back

True or False: Petechial hemorrhaging in the eyes occurs when vessels in the eye bleed because blood pressure increases in response to compression around the neck.

True

True or false: a decendent’s body at a crime scene (indoors with environmental temperature of 70 degrees F) has the onset of rigor mortis, and some observable lividity. the approximate time of death is at least 10 to 11 hours prior.

False.

true or false: the maggots and other insect infestation of the remains of a body may provide both an estimate of the time of death and evidence indicating whether a body has been moved.

True

how do you calculate the approximate time of death?

on the prompt it’ll state the temperature of the body when it was found, and state the time the body was found.

• take the normal body temp which is 98.6 F or 37 C.

• normal body temperature 37C - body temp of decreased = ____ C (how much temp has dropped)

• take ___C / 1.5 C = _____ hours

• take time body was found - ____ hours = time of death (AM or PM)

true or false: deductive reasoning is also referred to as inference.

True

blacklogs:

they refer to physical evidence that has been submitted to a laboratory for analysis but is waiting processing. this could be requested analyses of physical evidence, and individual items of evidence.

what is wrong with the CSI effect?

it refers to the impact of CSI programs that make a false idea of criminal justice systems in society. it makes the court process appear shorter than with it is, affects jurors opinions based off of shows they’ve seen, affects what tasks certain careers do, providing wrong information, and expect more from forensic testing.

• this includes police chief effect, educators effect, and victim effect

what are main sources/reasons of Backlogs?

• the demand for drug evidence because its a consistent source of workload for crime labs and is very time consuming and expensive.

• latent print request

• DNA analysis

crime scene investigator:

they are police officers trained in crime scene work or civilians trained as CSIs. they recognize, document, preserve, and collect physical evidence. after, they theorize what created the scene and reconstruct (scene → locate → preserve → test it → theorize)

what are the role for the first responding officer to a crime scene?

to secure the crime scene and go through ARISN

what does a judge use or do to determine if forensic evidence is dismissible?

they make sure that the evidence was not obtained through an unlawful search that is illegal.

Pallor mortis:

the first mortis to set in within 15-25 minutes after death. it is the paleness of the skin that occurs when the blood begins to sink towards the lowest part of the body which leaves upper skin surfaces pale.

what is Cadaveric spasm, what is the nickname for this, and when does it happen?

it is also know as the death grip, and it is the sudden stiffening of the muscles that happens at the exact moment of death. its common in suicide.

what is the procedure of a postmortem exam?

1) review medical history

2) initial exam

3) dissection and evidence collection

what happens in the 3 steps of post mortem exam?

1) review medical history: overview of medical history to determine possible natural causes, they want to know past surgeries, broken bones so they can eliminate information

2) initial exam: thorough exam of the external body such as fingernail, toenail scrapings, swabs, biological stains, fibers, hairs, eyes are all photographed and turned over to investigators.

3) dissection and evidence collection: the removal of all organs, and examine the brain. organs are weighed and dissected and run tests on blood, urine, interal organs, and DNA analysis to see if there were drugs or diseases.

toxicologist:

analyze bodily samples to determine toxins like drugs, alcohol, or posions

what are the two main signs of strangulation/asphyxia?

a fractured Hyoid bone (in the front of the neck), and hemorrhaging in the eyes.

this can happen from Manual strangulation which is done by the hands of a person. or from a Ligature which uses another object to strangle. or from drowning which can happen while conscious or unconscious.

forensic anthropology:

applies skeletal analysis and archeological techniques to solve criminal cases and identify remains

what can forensic anthropologist tell us?

they can determine age, sex, race, height, timeframe of death, type of trauma, and weight by looking at the ondontology, osteology. they look for postmortem alternations, and antemortem conditions.

post mortem:

an autopsy or medical examination of a body after death.

what are the 5 stages of decomposition?

stage 1, fresh stage: putrefaction(process of decay) begins immediately after heart stops. pallor mortis sets in within 15 minutes after death and caused by lack of circulation. blisters begin to form on the skins surface.

stage 2, Bloat: the gases being released from the cells breaking down enzymes and gets trapped in the body which causes the body to double in size. bacteria produces unpleasant odor and can linger long after body has been removed. insect activity will begin to be present.

stage 3. active decay: when the body loses all the liquid. cells are decomposing into liquid from the inside to outside. body begins to change color, and will eventually dry out. this is the most insect activity, such as blowflys are most common.

stage 4, Advanced decay: rate of decay decreases due to lack of left over materials and fluids. its “mummified” as skin breaks down, crumbles, and falls off.

stage 5, skeletal decay: only thing left is the skeleton now that all tissues and muscles are decayed. air, water, and other conditions play a role in how long skeletal decomposition occurs.

blow flies:

blow flies feed on carrion (decaying flesh) and will colonize. they do not pay eggs at night and may delay until the next morning. they are large metallic, blue and green and have 6 parts of their cycle.

prompt: at 11:00pm a decendents body (indoor with a room temp of 70 degrees F) has an internal liver temp of 29,5 degrees C. the approximate time of death is….

6pm is the approximate time of death.

what is the normal body temperature of a human?

37 degrees C or 98.6 F (for math we use Celcius)

how much does body temperature drop every hour?

drops 1.5 C every hour.

what does NASH mean and what are they?

it is the manners of death.

• Natural: disease, means you have no reason to continue investigation

• Accidental: trauma, investigation to see if there was any foul play

• Suicide: trauma and self inflicted

• Homicidal: trauma, where there could be a crime because sometimes its not a crime. for example, self defense

undetermined: not able to place a death in any of these categories

abductive reasoning:

combination of deductive and inductive reasoning, and then calculate something based of that combination. its most likely chain of evidence that created that crime.

direct evidence:

category of evidence, and is proof that establishes a fact without need of logical interference. such as a gun is recovered and has victims DNA, suspects DNA, and a confession)

inculpatory evidence:

category of evidence, it is information, object or testimony that includes a person in the crime or guilt in crime. this supports prosecutors case

exclusive evidence:

category of evidence, and is a piece or category of proof that points uniquely to a specific fact, conclusion or individual

what are the problems of backlogs?

• evidence submitted to labs have no intent to use or rly upon a laboratory analysis. when prosecutors choose to request that each item in a case be analyzed even though the particular item in question may not be essential but is submitted to be prepared for unpredictable requests from defense lawyers or juries.

• evidence for which analysis is no longer necessary due to settlement or other disposition. this is poor communication and ineffective information between police, labs, and prosecutors

• simulated or symbolic evidence collection. this is evidence that was collected, processed into evidence storage, but never analyzed.

how could backlogs impact public safety?

an offender who remains free to commit crimes as the evidence that could potentially be used to identify, apprehend, and prosecute remains unanalyzed

how has the CSI effect impacted the criminal justice system?

prosecutors, defense attorneys, and judges report that they have had to change their court strategies to account for jurors increased expectations of forensic evidence, BUT DOES NOT typically affect the jurors final verdict.

what are the 5 steps crime scene processing?

1) first responder secure and isolate scene and starts defining the crime scene.

2) conduct an initial scan and walkthrough of scene. locate, identify crime, environment factors, and start planning the processing of the crime.

3) crime scene documentation. intense documentation of scene with photography, video recording, observations, rough sketch, written records of notification like arrival, victim description, crime scene team, actions taken and evidence identified

4) crime scene search which is done after documentation but prior to collection of evidence. involves search patterns, field testing (swabbing to figure out substances)

5) collecting and packaging evidence. important to collect as soon as other steps are done to avoid lost evidence or messing with evidence. its important to carefully label and seal.

what is ARISN?

the steps first responding officers go through, in order of priority.

1) Approach scene with caution, and alert for persons and vehicles leaving vicinity, note for descriptions and communicate the information.

2) Render first aid. provide aid to victim first. then begin noting of locations and conditions of victim, weapons or other contributing factors.

3) Identify additional victims and potential witnesses. this is the initial canvas of immediate area

4) Secure the crime scene. identify boundaries of the crime scene and secure it. this includes setting up barriers and perimeter control, check area for safety or possible individuals in area, and identifying exits and entrances around the scene.

5) Notify other appropriate authorities. call for investigators, animal control, child protective services, etc.

odontology:

the examination of teeth, and forensic anthropologist must know how to look at dental records to find identity of victim

osteology:

forensic anthropologist need to know the study of bones like humans skeletons.

antemortem trauma:

trauma that happened before death like fractures. this is done by forensic anthropologist

perimortem trauma:

this is done by forensic anthropologist, and is what happened at the death, such as an injury at or near time of death like dismembering body, or wildlife chews up bones.

taphonomic context and assessment.

immediate environment and surroundings where the body is found. then an assessment is done which is the documentation of condition of body. such as how long its been there, what happened since death, drying and bleaching by weather, wildlife changes, stage of decomposition. this step is apart of recovering remains.

timeline of human decomposition:

human decomposition starts → 24-72 hours after death internal organs decompose → 3-5 days after death bloat starts → 8-10 days after death body turns from green to red → several days later nails/teeth fall out → 1 month after body liquifies → 1 year later skeleton decomposes

what is the life cycle of a blow fly?

1) females lay eggs on open wounds or on natural orifices (soft payer that is easy to break).

2) the eggs hatch within 23 hours into a larva, and takes 27 hours to molt

3) the molted larva takes 22 hours to grow larger

4) then the large larva takes 130 hours to enters the pupal stage

5) once in the shell, it takes 143 hours to match and emerge as a adult fly

6) has become a fly and typically lays eggs in same area

what can the toxicologist tell us after testing a insect?

the insects feed on carrion which is the tissue, and the tissue contains toxins in the body. if a maggots ingest tissue, its stored in their crop or food storage organ, and the material inside this crop is a source of the hosts DNA and can identify the parent drug that the host consumed.

prompt: a killer leaves an original site of a crime scene for a few days, letting blowfly eggs in the wounds, corner of eyes, and nostrils. the killer returns and moves it to a new site/secondary crime scene that has a different environment. when its in the new dump site, it will attract insects local to the area. how can an entomologist use these to different types of bugs to help figure out the original location of the body?

if there are two different kinds of bugs that are from two very different environments, it can show that where the body was found was not where the action occured.

how is it possible for the puparia case to show how long a body has been there?

when the larvae hatches, it leaves behind the dark puparia case which shows the cycle was completed. if you understand the cycle and time it takes, it helps determine a rough TOD.

entomology:

the study of insects and forensic entomologist can evaluate the state of insect colonization to estimate how much time has elapsed since their arrival or the minimum elapsed time since death, also called the minimum PMI

exclusionary rule:

came from the Mapp v Ohio 1961 case. the rule states that if evidence is seized with force or going against 4th amendment law, then no evidence will be used in court because its going against out consititutional rights.

fruit of posioness tree doctrine:

made by the US supreme court that says evidence that was illegally seized, anything that comes from that root or discovery of evidence cannot be used in a case

what are the two methods of estimating minimum elapsed time since death?

1) larval dipteria (flies): known passage of time when the first egg is laid on the remains until the first adult flies emerge. occurs within a few hours to several weeks by looking at cycle

2) carrion insects: feeding on the body and have successional colonization and shows minimum time elapsed since death. this occurs weeks after death until dry bones remain

how else can insects link a suspect?

insects like bedbugs and fleas can link suspects to a room by analyzing those bugs that could’ve bit a suspect.

what do judges look at when challenges arise or if evidence should be used?

• they ask if the piece of evidence is relevant.

• how beliveable evidence is so quality or quantity of evidence

• presumptions or is there a conclusive statement

• was there an interference or obstruction of the legal procedure

• was there Hearsay (someone else testifying that someone else told them something.

what are examples of causes of death?

gunshot wound to the chest, blunt force trauma to the head, drug intoxication,

what are examples of mechanism of death?

brain swelling, fatal blood loss, hemorrhage. they often are named scientifically or said with detail like these.

what are examples of manner of death?

NASH: natural, accidental, suicide, homicide and undetermined

coroners:

most often an elective official and do not need medical background to become one. coroners do death certificate, and determines if an autopsy is require, and can determine the mechanism and cause of death based off of observations.

medical examiners:

medical doctors, skilled in determining mechanism and cause of death, and do a thorough autopsy.

what is a mechanical trauma?

the broadest categories caused by external forces like gunshot wounds, bludgeoning, stabbings, car accidents.

low velocity vs high velocity:

low velocity has a low speed such as bludgeoning or hitting someone with an object. high velocity is high speed like a gunshot.

penetrating vs perforating:

they are both gunshot wounds but penetrating enters the body and remains lodged inside. a perforating is a gunshot bullet that leaves an entry and exit wound.

public symphysis:

shows age and sex of development of adults and is the most reliable indicator of age.

by looking at the pelvic bone, how can you tell the difference between female and male?

male has an acute angel pelvic, while females have a wider and larger opening on their pelvic for giving birth.

equifinality:

a trauma that is mocked by another mean and makes it hard to determine the cause of death. for example, there could be punctures on a skeletal remain but it could look like cut marks from a knife or an animal that chewed on the bones.

forensic entomologist:

study of insect evidence and can test insects for toxins, estimate time of death, location of death based off insects.