CRIMINALISTICS CHAPTER 3 PHYSICAL EVIDENCE

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

COMMON TYPES OF PHYSICAL EVIDENCE Lists and definitions or examinations

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

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

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

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

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

FINGERPRINTS Latent or other prints Establish identity Place at scene

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

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

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

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

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

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

PLASTIC BAGS Identification Comparison to known Fracture match

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

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

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

TOOL MARKS Usually under firearms Impressions made by tool

LIGHTS Mainly vehicle Conducted to determine on/off during crash

WOOD Other vegetative material Comparison To link suspect to scene

PHYSICAL EVIDENCE IDENTIFICATION COMPARISON

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)

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

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

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

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

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

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

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

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

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

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

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

COMPARISON OF KNOWN AND UNKNOWN

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.

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

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

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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

CRIME SCENE RECONSTRUCTION PHYSICAL EVIDENCE CRIME SCENE RECONSTRUCTION

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

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

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

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

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

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)

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

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”

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