What are three general types of crime scene evidence?

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TitleWhat are three general types of crime scene evidence?
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  1. What are three general types of crime scene evidence?

Answer: (page 86)

Biological evidence, impression evidence, and manufactured items.

21. What factors affect the gun powder stains left on a piece of clothing or other physical evidence?

Answer: (page 85)

Type of gun fired, type of material receiving the powder stain.

22. List and define the two methods used by forensic scientists when examining physical evidence.

Answer: (page 86)

Identification and comparison. Identification is the process of determining a substance’s physical or chemical identity. Comparison is the process of ascertaining whether two or more objects have a common origin.

23. To permit positive identification, testing procedures used by a forensic scientist must meet what two conditions?

Answer: (page 87)

Testing procedures must give characteristic results for specific standard materials. In addition, the number and type of tests required to positively identify a substance must be sufficient to exclude all other substances.

24. Describe the two steps in the process of comparison. What question does each step answer?

Answer: (page 87)

The first step in comparison is determining which properties from the suspect and the standard/reference specimen to compare. This step attempts to determine whether the two samples are the same. The second step is concluding the origins of the specimens. This step attempts to determine how likely it is that two samples came from the same source.

25. Define individual and class characteristics.

Answer: (page 88)

Individual characteristics are properties of evidence that can be attributed to a common source with an extremely high degree of certainty. Class characteristics are properties of evidence that can be associated only with a group and never with a single source. Examples include paint and fibers.

26. Define product rule.

Answer: (page 90)

The product rule states that one can obtain an overall frequency of occurrence for a genetic profile by multiplying together the frequencies of independently occurring genetic markers. If several different factors from two blood samples are found to be identical, a forensic scientist can apply the product rule to calculate how frequently blood containing that combination of factors occurs in the population. The more blood factors that match, the greater the probability that the two blood samples originated from a common source.


27. What is the greatest weakness of class evidence? List two factors that contribute to this weakness.

Answer: (page 91 )

The examiners can’t assign exact or even approximate probability values to the comparison of most class evidence. Few statistical data exist from which to derive comparative information for most class evidence, and society is increasingly dependent on mass-produced products that are extremely difficult to distinguish from one another.

28. What is the value of class evidence? Why is this important in making a case to a jury?

Answer: (page 92)

The value of class evidence lies in its ability to corroborate events with data that are , as nearly as possible, free of human error and bias. This is important because most other types of evidence (such as eyewitness testimony and confessions) are subjective and susceptible to dispute, human error, or bias.

29. Why are some jurists wary of allowing unconditional use of scientific evidence in court?

Answer: (page 93)

Because juries often accord scientific evidence greater weight than other evidence, tend to consider it more trustworthy, and often view it with less skepticism. Without proper safeguards, the use of scientific evidence may unfairly prejudice a case against the accused.

30. How can the extreme sensitivity of modern analytical techniques hinder the process of comparing items of physical evidence?

Answer: (page 94)

When measured or examined with extreme precision, no two items-even those originating from the same source---are exactly alike. Thus, using an analytic technique that is too sensitive makes it impossible to meaningfully compare different items of evidence.


31. How does a magnifying glass enlarge objects viewed through it?

Answer: (page 265)

A magnifying glass makes things appear larger by refracting, or bending light rays as they pass from the air into the glass and back into the air.

32. Why does a compound microscope produce greater magnification than a magnifying glass? How does the eyepiece lens contribute to magnification?

Answer: (page 256)

Because it uses two lenses to enlarge the object being viewed instead of just one. The eyepiece lens magnifies the real, enlarged image created by the objective lens, producing a greatly enlarge virtual image of the object.

33. How does one calculate the magnification power of a compound microscope?

Answer: (page 260)

The total magnification power of a compound microscope is the product of the magnifying power of each lens.

34. Why might an examiner choose a microscope with a lesser magnification to study a specimen?

Answer: (page 260)

As magnifying power increases, the microscope’s field of view--- the size of the specimen it can study----decreases. The microscopes depth of focus----the thickness of the specimen it can study---also decreases with increasing magnification. An examiner might first select a lower-magnification microscope to get a good general overall view of the specimen, then switch later to a higher-power microscope to study smaller portions of the specimen in more detail.

35. Briefly describe how a comparison microscope works and what it is used for.

Answer: (page 261)

The comparison microscope is two compound microscopes connected by a bridge that uses mirrors and lenses to combine the images from two objective lenses into a single image. A comparison microscope is used to make side-by-side comparison of specimens.


36.List two unique characteristics of the stereoscopic microscope

Answer: (page 263)

It presents a three-dimensional image of an object. Also, whereas the image formed by the compound microscope is inverted and reversed, the stereoscopic microscope forms a right-side-up image.

37. What is the most widely used microscope in the crime laboratory? What features make it particularly suited for examination of physical evidence?

Answer: (page 263)

The stereomicroscope. Its wide field of view and great depth of focus make it an ideal instrument for locating trace evidence. Its large working distance (the distance between the objective lens and the specimen) makes it ideal for microscopic examination of big, bulky items.

38. What happens to a light beam that passes through a polarizing crystal? What happens when plane-polarized light passes through a second polarizing crystal set perpendicular to the first crystal?

Answer: (page 265)

A beam of light passing through a polarizing crystal emerges vibrating in only one plane. When plane-polarized light passes through a second polarizing crystal set perpendicular to the first crystal, the light is blocked by the second crystal. Light that is confined to a single plane of vibration is said to be plane-polarized.

39. Explain how the infrared microspectrophotometer identifies a specimen. What type of physical evidence is the microspectrophotometer typically used to analyze?

Answer: (page 267)

The infrared microspectrophotometer identifies a specimen by obtaining its IR spectrum, which is unique for every chemical substance. The technique is used to analyze fibers and paints.

40. What is the main advantage of the microspectrophotometer?

Answer: (page 267)

The microspectrophotometer allows the forensic scientist to view a particle under a microscope while obtaining its absorption specrum. This provides added information to help characterize trace quantities of evidence.

41. How can a scanning electron microscope be used to determine whether a suspect has recently fired a gun?

Answer: (page 271)

Possible gunshot particles remaining on a shooter’s hands are lifted off with a piece of adhesive tape; the tape is then examined under the scanning electron microscope. The X-rays produced by the particles are analyzed and displayed according to their energies. This allows the examiner to detect elements frequently found in bullet primers.


42. What do each of the following acronyms stand for; IAFIS, CODIS, NIBIN, PDQ, and SICIR?

Answer: (page 95)

IAFIS = Integrated Automated Fingerprint Identification System

CODIS = Combined DNA Index System

NIBIN = National Integrated Ballistics Information Network

PDQ = International Forensic Automotive Paint Data Query

SICAR = Shoe Image Capture and Retrieval

43. What information can be obtained from the following data bases; IAFIS, CODIS, NIBIN, PDQ, and SICIR?

Answer: (page 95)

IAFIS = a national fingerprint and criminal history system maintained by the FBI.

CODIS = allows federal, state, and local crime labs to electronically exchange and compare DNA profiles.

NIBIN = allows firearm analysts to acquire, digitize, and compare markings made by a firearm on bullets and cartridge casings.

PDQ = contains chemical and color information pertaining to original automotive paints.

SICAR = a commercially available shoeprint database.

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