Chapter 7 Crime Scene Evidence & Experiments

Question 1

Explain what should be done to protect evidence at a crime scene, and list three things that should be done to document the scene before evidence is removed.

Answer 1

Restricting access to the area prevents people from stepping on evidence, handling it, or removing it from the scene. No one should be allowed to try to clean up the area before the investigation is completed because evidence could be destroyed.
The three things that should be done to document the scene before evidence is removed is:
1. sketching the location
2. making detailed notes
3. taking photographs

Question 2

What scientific tests are most commonly introduced in criminal trials?

Answer 2

DNA
Analysis of controlled substances
Toxicology

Question 3

Define chain of custody, and explain how it is maintained for trail.

Answer 3

Recored of each person who has handled evidence. They will need to testify in order to show the judge and jury that the evidence has not been tampered with.

Question 4

What foundation must be laid for the admission of a piece of evidence found at the crime scene? For the admission of the results of a scientific test?

Answer 4

Foundation for admission of a piece of evidence

1. Show the opposing council before testimony is introduced
2. Assign it a number/letter
3. Call a witness to lay the foundation
4. Request it to be admitted into evidence by judge

Admission for scientific tests involves answering the following three questions:

1. Is this a valid scientific test?
2. Was accurate equipment used for the test?
3. Was the test performed in an appropriate manner by a qualified person?

Question 5

Explain the scientific basis for fingerprint identification.

Answer 5

1. Fingerprint is an individual characteristic
2. Fingerprints remain unchanged during an individual’s lifetime
3. Fingerprints have general ridge patterns the permit them to be systematically classified.

Question 6

Explain the reason why blood test can accurately show alcohol level in the body.

Answer 6

Alcohol is rapidly absorbed into the blood & circulatory system from the stomach and small intestine. Alcohol crosses cell membranes by a simple diffusion process and quickly achieves equilibrium in the body. The result is that alcohol rapidly becomes associated with all parts of the body in concentrations proportionate to body water content. It is therefore possible to estimate the total alcohol content of the body using a small sample.

Question 7

Explain what can determined by conducting scientific tests on bullets and cartridges.

Answer 7

Microscopic examinations can reveal the caliber of the gun that fired the cartridges & many facts about the barrel of the weapon involved.

Question 8

Explain how DNA testing can be used to identify the defendant as the person who committed the crime.

Answer 8

Identical DNA molecules are found in each cell of a person’s body. With the exception of identical twins, each individuals DNA is unique.

Question 9

Explain why the courts rarely admit polygraph test results and seldom permit witness to testify after having been hypnotized.

Answer 9

Courts distrust polygraphs results because of the high frequency of inconclusive results.

Hypnosis is unreliable.

Question 10

Define experiment and give two examples of experiments that could be used in criminal trials.

Answer 10

Ideal experiment screens out all extraneous variables so that the experimenter can measure the impact of one factor.

Going to the crime scene under lighting conditions that are similar to those the existed at the time of the crime to determine if the stop sign is visible.

Have someone walk to from one location to another to determine if it is possible to cover the distance in the time stated by the defendant.