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CRIMINALISTICS CHAPTER 3

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Presentation on theme: "CRIMINALISTICS CHAPTER 3"— Presentation transcript:

1 CRIMINALISTICS CHAPTER 3
PHYSICAL EVIDENCE

2 PHYSICAL EVIDENCE Impossible to list all items that could be important at crime scene\ Practicle to list those that scientific examination can yield significant results Investigator needs to be familiar with Recognition – Collection – analyses – Laboratory procedures and capabilities

3 COMMON TYPES OF PHYSICAL EVIDENCE
Lists and definitions or examinations

4 BLOOD, SEMEN & SALIVA All suspected saples
Liquid or dried Animal or human Subjected to serological examination (DNA) to determine: Identity Origin

5 DOCUMENTS Handwriting or Typewriting Related Items
Determine authenticity or Source Related Items Paper Ink Indented writing Obliterations Burned or Charred documents

6 DRUGS Controlled substances seized in violation of the law Sale
Distribution Manufacture Possession

7 EXPLOSIVES Devices containing explosive charge
Residue from scene of explosion to examine for suspected explosive charge

8 FIBERS Natural or synthetic fibers
Transfer may be helpful in establishing relationship between objects/persons

9 FINGERPRINTS Latent or other prints Establish identity Place at scene

10 FIREARMS Firearms, Projectiles, cartridges Firearms residue Identify
Compare To other exemplars To firearms Firearms residue Present? Distance & angle

11 GLASS Glass particles or fragments Window panes with holes
Transfer evidence Window panes with holes Sequence & origin Broken windows Characteristics

12 HAIR Animal or human Origin Race Body area Comparison Root present DNA

13 IMPRESSIONS Tire or Shoe prints in soft material Fabric Impressions
Bite marks

14 PAINT Liquid or dried Transfer from one surface to another
Identification Comparison

15 PETROLEUM PRODUCTS Arson Oil or grease stains
Residues identified at fire scene (accelerants) Oil or grease stains Comparisons to place at scene

16 PLASTIC BAGS Identification Comparison to known Fracture match

17 POLYMERS Plastic, Rubber, etc Identification
Comparison to objects at scene

18 SERIAL NUMBERS Usually falls under firearms Stolen property
Defaced serial numbers restored

19 SOIL AND MINERALS Link a person or object to location Examples
Soil found on clothing or vehicles Soil found on tools

20 TOOL MARKS Usually under firearms Impressions made by tool

21 LIGHTS Mainly vehicle Conducted to determine on/off during crash

22 WOOD Other vegetative material Comparison To link suspect to scene

23 PHYSICAL EVIDENCE IDENTIFICATION COMPARISON

24 MATHEMATICAL PROBABILITY
Underlies virtually every human action Based on idea that the outcome of an event can be logically estimated Estimate based on known conditions, past performance , & experience with similar events Familiar example (coin toss)

25 PROBABILITY Blood as example Four major types O 40% 8:20 A 40% 8:20
Any blood stain must be one of these types

26 Probability Significance Probability of occurrence of different types
Ex: O is 8 times more common than AB If O found fewer people eliminated than if AB is found AB sample is therefore higher quality evidence than type O

27 Probability The greater the frequency of occurance the less significance attached Must also consider concept of Mutually Exclusive Events that by nature preclude other events Not possible for individual to have two types Therefore if type A found at scene the blood did not come from person with any other type

28 PROBABILITY Some forms of physical evidence do not lend themselves to statistical evaluation Example: Do not know statistical probability of a particular configuration of a toolmark Value must be estimated base on experience Must form an opinion as to value of evidence

29 PROBABILITY Experience has shown that microscopic relationships between the impression and the tool are so specific to be unique The basis of the opinion must be experience that equips the examiner to note the unique points that distinguish the item from a larger body of occurances

30 IDENTIFICATION Definition
The determination of the physical or chemical identity of a substance with as near absolute certainty as existing analytical techniques will permit

31 IDENTIFICATION EXAMPLES
Suspected drug sample identified to contain cocaine Residues from a fire identified to contain gasoline Sample found at scene identified as blood May determine species Vegetable material identified as type of wood

32 IDENTIFICATION 1.Adoption of standard testing procedures
must give characteristic results for standard testing materials Testing permanently established used to establish identity test results must be same on unknown as on a known sample

33 IDENTIFICATION 2. The number and type of tests must be sufficient to exclude all other substances Must devise an analytical scheme that will eliminate all but one substance If identify white powder as cocaine must exclude every other drug

34 IDENTIFICATION No simple rules as to what constitutes thorough and foolproof analytical scheme Each type of evidence requires different type of tests Some may be identified with one test, some may require many Little or no control over the quality or quantity of samples submitted

35 IDENTIFICATION The forensic scientist must conclude in many cases:
What point the analyses is concluded The criteria for positive identification Conclusion beyond reasonable doubt for court Most disciplines have SOP

36 COMPARISON OF KNOWN AND UNKNOWN

37 COMPARISON Definition
An analysis that subjects a suspect speciman and a standard/reference specimen to the same tests and examinations for the ultimate purpose of determining whether or not they have a common origin.

38 COMPARISON Examples Place a suspect at scene by noting similarities between hair found at scene to known hair of suspect Similar to or consistent with and could have a common origin

39 COMPARISON Examples Place vehicle at scene of hit and run by noting similarities between paint found on victim clothing and known paint from vehicle Chemical and physical property match could have common origin Fracture match have a common origin

40 COMPARISON Forensic comparison two step process
1. Combinations of select properties are chosen from the suspect and the standard/reference specimen for comparison How many properties are chosen depends on the type of material Overriding consideration must be the ultimate evidential value of the conclusion

41 COMPARISON 2. When examination is completed the examiner must be prepared to render a conclusion with respect to the comparison Do they come from same source If one property does not agree, no common origin If all properties compared agree are they from common origin (not necessarily)

42 COMPARISON Physical match
The most definite point of comparison between objects Example – point of screwdriver and shaft from which it broke Any item that suggests a rip, tear, or breakage should lead to a search for its counterpart

43 INDIVIDUAL CHARACTERISTICS
Definition Evidence that can be associated with a common source with a high degree of probability Examples Matching ridge characteristics of two fingerprints Matching striations on bullets Matching irregular and random wear patterns on footwear

44 INDIVIDUAL Not possible to state with mathematical exactness the probability that specimens are of common origin. (exception DNA) Conclusion that probability is so high as to defy mathematical calculations or human comprehension INDIVIDUAL Example – Fingerprints Several mathematical models proposed One model – probability of two individuals with same fingerprint 1 x 10 followed by 60 zeros Practical – millions of prints compared over 100 years never found two the same

45 RARITY Exceptional circumstances connected with the place, time or general conditions under which physical evidence is discovered can heighten its quality Example: A hairpin found near murdered wonam may not be of as much value as a mans tie clasp

46 CLASS CHARACTERISTICS
Definition Properties of evidence that can only be associated with a group and never with a single source Disappointments when Lab unable to relate evidence to a common source with a high degree of probability

47 CLASS CHARACTERISTICS
Weakness Inability of examiner to assign exact or approximate probability values to the comparison of most pyhsical evidence Scientist attempt to creat or update statistical databases when possible Mostly forensic scientist must rely on personal experience to interpret significance of comparison

48 CLASS CHARACTERISTICS
Efforts made to find individual evidence Fingerprints, DNA, Firearms match Most physical evidence is class match Majority of evidence in case is subjetive Eye witness, confessions, informant Physical evidence provides corroboration

49 CLASS CHARACTERISTICS
Trying to find define the significance of class evidence in exact mathematical terms is difficult if not impossible Class evidence by definition is not unique Only objects that exhibit a significant amount of diversity are appropriate for physical evidence colored fibers v. white cotton

50 CLASS CHARACTERISTICS
Must provide evidence that would convince a reasonable man that there is no other explanation Dealing with more than one type of physical evidence, their collective presence leads to a high degree of certainty

51 CLASS CHARACTERISTICS
Must consider reality in courtroom Weight or significance left entirely to jury Lay people usually give scientist high degree of significance Scientific testimony takes on more reliability in courtroom Given great weight in deliberations

52 PHYSICAL EVIDENCE When does class characteristic become individual characteristic Source of debate and disagreement EXAMPLES How many striations to match bullet How many paint layers to individualize How many ridges to match fingerprint

53 PHYSICAL EVIDENCE Find as many characteristics as possible to compare substances Significance decided by Quality of evidence Composition of evidence Case history Examiners experience Conclusion can reach from speculation to near certainty

54 PHYSICAL EVIDENCE Properties and characteristics Practical limits
Extreme – No two things are alike in every detail Modern analytical techniques have become too sensitive in some cases Learning how to use instruments part of work Proficiency to interpret findings critical

55 CRIME SCENE RECONSTRUCTION
PHYSICAL EVIDENCE CRIME SCENE RECONSTRUCTION

56 CRIME SCENE RECONSTRUCTION
Team event Reconstruct events that occurred Prior to crime During crime Subsequent to crime Collaborative effort including Law enforcement, criminalist, Medical examiners

57 RECONSTRUCTION All professionals bring unique perspective
Try to answer questions about crime How many people involved Cause of death Was there an attempt to cover up Physical evidence plays critical role in reconstructing events

58 RECONSTRUCTION Physical evidence can
Support accounts given by witnesses/suspects Contradict accounts given by witnesses/suspects Generate leads Confirm reconstruction to jury Physical evidence is the foundation of reconstruction

59 RECONSTRUCTION Actions law enforcement must take to optimize reconstruction 1. Crime scene protection and security A continuous process (beginning to end) Evidence can be destroyed by walking through There is the possibility of contamination from persons allowed in the scene

60 RECONSTRUCTION 2. Preliminary examination
See scene as left by perpetrator Experience and physical evidence critical Captures nature of scene Hypothesize what happened Document observations Determine how scene should be worked

61 RECONSTRUCTION 3. Involve other professionals Medical examiners
Position of body Injuries Has body been moved Clothed before or after death Cause of death Estimate of time of death (not very accurate)

62 RECONSTRUCTION 3. Other professionals Criminalists
Approximate bullet path (lasers) Blood spatter analysis (chapter 12) Glass penetration (Chapter 4) Gunshot residue for distance (Chapter 15)

63 RECONSTRUCTION From text
“Reconstruction supports a likely series of events by the observation and evaluation of physical evidence, as well as statements made by witnesses and those involved with the incident”

64 RECONSTRUCTION Team effort Put together different pieces of the puzzle
Need right connections to show relationship between victim, suspect, and crime scene Can play a vital role in helping jury arrive at proper verdict

65

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