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Questions and Answers
A detective is working a new case and needs to estimate the time of death. Which of the following mortis processes would be MOST useful in the initial hours after death?
A detective is working a new case and needs to estimate the time of death. Which of the following mortis processes would be MOST useful in the initial hours after death?
- Rigor mortis, due to its onset approximately 2 hours after death and progression over the first day. (correct)
- Algor mortis, due to its constant and predictable rate of body cooling, regardless of environmental conditions.
- Livor mortis, due to its immediate onset and clear indication of the pooling of blood.
- The presence of insect activity on the corpse, as insects colonize a body very rapidly after death.
In forensic science, what is the primary role of hemoglobin in the Kastle-Meyer test, and what does a positive result indicate?
In forensic science, what is the primary role of hemoglobin in the Kastle-Meyer test, and what does a positive result indicate?
- Hemoglobin acts as a reducing agent, neutralizing any other substances present and confirming blood through the absence of other reactions.
- Hemoglobin acts as an inhibitor, preventing the reaction and indicating the absence of blood if the solution remains colorless.
- Hemoglobin acts as a catalyst, accelerating the reaction between phenolphthalein and hydrogen peroxide, resulting in a color change that indicates the presence of blood. (correct)
- Hemoglobin acts as a pH buffer, stabilizing the solution and confirming the presence of the tested substance through consistent pH levels.
How do forensic investigators utilize STR analysis in DNA profiling, and what makes it a reliable method for identifying individuals?
How do forensic investigators utilize STR analysis in DNA profiling, and what makes it a reliable method for identifying individuals?
- STR analysis targets and amplifies highly variable regions of non-coding DNA, providing a statistical likelihood of unique matches with minimal error. (correct)
- STR analysis sequences entire genomes to catalog all genetic variations, providing an absolute identification of individuals with certainty.
- STR analysis identifies unique mRNA sequences that dictate individual traits, allowing for precise differentiation based on gene expression.
- STR analysis examines single nucleotide polymorphisms (SNPs) to pinpoint specific genetic mutations that distinguish individuals on a broad scale.
Why is enhancing the resolution of security camera footage in crime shows often an unrealistic portrayal of forensic capabilities?
Why is enhancing the resolution of security camera footage in crime shows often an unrealistic portrayal of forensic capabilities?
What is the MOST significant limitation of relying solely on algor mortis to estimate the time of death, and how do medical examiners address this limitation in practice?
What is the MOST significant limitation of relying solely on algor mortis to estimate the time of death, and how do medical examiners address this limitation in practice?
How does the presence or absence of livor mortis provide information about a body's position after death, and what does it indicate if livor mortis is fixed?
How does the presence or absence of livor mortis provide information about a body's position after death, and what does it indicate if livor mortis is fixed?
What is the role of facial recognition technology in forensic investigations, and what type of data does it analyze to identify potential suspects?
What is the role of facial recognition technology in forensic investigations, and what type of data does it analyze to identify potential suspects?
What academic backgrounds are typically required for forensic investigators and medical examiners, respectively, and why are these specific degrees necessary?
What academic backgrounds are typically required for forensic investigators and medical examiners, respectively, and why are these specific degrees necessary?
How does the legal system view forensic evidence, and what is the ultimate goal of forensic analysis in the context of a trial?
How does the legal system view forensic evidence, and what is the ultimate goal of forensic analysis in the context of a trial?
In the Chicago case study, the time-stamped soda receipt places Bob at a store at 5 PM, but the medical examiner estimates his time of death to be between 5 PM and 7 PM. What conclusions can investigators draw from this information, and what investigative steps should they prioritize?
In the Chicago case study, the time-stamped soda receipt places Bob at a store at 5 PM, but the medical examiner estimates his time of death to be between 5 PM and 7 PM. What conclusions can investigators draw from this information, and what investigative steps should they prioritize?
Flashcards
Forensics
Forensics
The use of science in law, particularly criminal law, to analyze evidence.
Livor Mortis
Livor Mortis
The pooling of blood after death, causing skin discoloration.
Rigor Mortis
Rigor Mortis
The stiffening of muscles after death due to lack of ATP.
Algor Mortis
Algor Mortis
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Image Enhancement Limitations
Image Enhancement Limitations
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Faceprint
Faceprint
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Kastle-Meyer Test
Kastle-Meyer Test
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STR Analysis
STR Analysis
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Study Notes
Forensics in Crime Shows
- Police procedurals offer a glimpse into science, specifically forensics.
- Forensics involves using science in law, particularly criminal law.
- Forensic investigators analyze crime scenes, run lab tests, and specialize in areas like DNA or bullets.
- Investigators need a science degree (chemistry, biology, or forensic science).
- Medical examiners require a medical degree.
- The aim of forensics is to gather and analyze evidence for court use.
Hollywood vs. Reality in Forensics
- Crime shows often exaggerate or misrepresent forensic science for entertainment.
- Real-life forensic tests are not as fast or accurate as depicted in shows.
- Technology used in crime shows is often unrealistic.
- The following hypothetical case study will explore practical forensics.
Case Study: Death in Chicago
- A dead man, identified as Bob, is found in an alley in Chicago at 11 PM.
- Bob has a receipt for soda from a nearby store, time-stamped at 5 PM.
Estimating Time of Death: Livor Mortis
- Medical examiners use several "mortis" checks to determine time of death.
- Livor mortis is the pooling of blood due to gravity after death, causing skin discoloration.
- If the body has been dead for over 12 hours, the blood coagulates and stays in place even if the body is moved.
- Bob's blood is still liquid, indicating he died less than 12 hours ago.
Estimating Time of Death: Rigor Mortis
- Rigor mortis involves the stiffening of muscles after death.
- Muscles require energy (ATP) to relax.
- After death muscles stiffen because they can't un-contract.
- Rigor mortis begins about 2 hours after death and lasts up to 36 hours.
- Bob exhibits rigor mortis, so death occurred more than 2 hours ago.
Estimating Time of Death: Algor Mortis
- Algor mortis is the cooling of the body after death, typically at a rate of 1.5 degrees Celsius per hour.
- Bob's rectal temperature is 29 degrees Celsius.
- Normal body temperature is 37 degrees Celsius, so Bob has lost 8 degrees.
- This suggests he has been dead for about 6 hours.
- The cold Chicago evening (5 degrees Celsius) accelerates heat loss, making time-of-death estimation difficult.
- Medical examiners estimate Bob's time of death between 5 PM and 7 PM.
Analyzing Security Camera Footage
- Detectives review security footage from the convenience store.
- The footage reveals someone following Bob when he left the store.
- The stalker's face is pixilated and blurry.
Image Enhancement in Reality
- Enhancing a blurry image is not possible in real life.
- Digital images are recorded as pixels, each representing an average color within a space.
- Once the color is stored as an average, the original color composition cannot be determined.
- An 8-megapixel camera captures 8 million pixels in an image.
- Zooming in on a distant object may result in blocky, undefined squares due to pixel averaging.
Facial Recognition and Databases
- The person following Bob returns to the store three hours later, wearing the same clothes.
- Detectives obtain a close-up picture and use facial recognition to identify him.
- Facial recognition relies on unique human facial features (curvature of eye sockets, distance between nose and mouth).
- Measurements of facial features form a faceprint.
- Databases of faceprints, like mugshots, are used for comparison.
- The FBI is developing a large biometrics database, but searchable databases are usually local.
- Chicago has a local faceprint database called NeoFace.
Identifying the Suspect: Charlie
- The suspect's faceprint matches a mugshot in the Chicago police database.
- The suspect is identified as Charlie, a hardware store owner.
Kastle-Meyer Test for Blood
- Investigators find a wrench with a red stain that they suspect is the murder weapon.
- They swab the stain and perform a Kastle-Meyer test to check for blood.
- The test involves adding phenolphthalein and hydrogen peroxide to the swab.
- If blood is present, hemoglobin acts as a catalyst, causing the phenolphthalein to turn pink.
DNA Analysis and STR
- If the Kastle-Meyer test is positive, the wrench is taken to the lab for DNA analysis.
- DNA analysis compares the blood on the wrench to Bob's DNA.
- Forensic teams use STR analysis to match DNA samples.
- STR analysis examines 13 sections of repeating base-pair patterns in DNA.
- The odds of two people having the same base pairs in all 13 sections are about one in a billion.
- STR analysis takes less than 90 minutes to run.
Connecting the Suspect to the Crime
- The DNA analysis shows the blood on the wrench belongs to Bob, making Charlie a strong suspect.
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