Crime Scene Investigation and Reconstruction

Crime Scene Investigation and Reconstruction. Fourth edition.

Introduction (1 of 2). In France, Edmond Locard, director of the Institute of Criminalistics in Lyons, described the theory that when two objects came into contact, there would be a cross-transfer of traces of materials. His theory became known as the Locard exchange principle, a central theme in the forensic sciences, especially those dealing with trace evidence (hairs, fibers, soil, etc.)..

Introduction (2 of 2). Reconstruction is a procedure may involve the reconstruction of a single event. Reconstruction of the crime scene frequently allows the investigator to determine the accuracy of statements from witnesses..

Types of Evidence. Direct Circumstantial Testimonial Physical.

Direct Evidence. Evidence that proves a fact without the necessity of an inference or a presumption, and, when true, conclusively establishes that fact.

Circumstantial Evidence. Involves a series of facts that, although not the fact at issue, tends, through inference, to prove a fact at issue This type of evidence is usually a set of circumstances from which an assumption can be made.

Testimonial Evidence. Evidence given by a lay person or expert witness The main issue for this type of evidence is credibility of the witness.

Physical Evidence. Physical objects that are linked to the commission of a crime Can be any type of physical object To be of any value it must be recognized as potential evidence, collected in an appropriate manner, and preserved properly.

Primary Roles of Physical Evidence. Reconstruction of the crime scene Determines whether or not a crime occurred Links an individual with another individual or with a crime scene (Locard exchange principle) Provides investigative leads to investigators Provides facts to a jury to assist in determination of guilt or innocence Provides evidence to link serial homicide or rape cases.

Advantages of Physical Evidence. Provides a tangible object for the jury to see The physical evidence can be taken into the jury room The defendant cannot distort the physical evidence.

More Advantages of Physical Evidence. Some cases cannot be solved without the physical evidence Physical evidence is not subject to memory loss The evidence can be tested by an independent expert.

Major Categories of Physical Evidence. Fingerprints Firearms Biological Trace Document Physical matching Toxicology Drug Other types.

Class vs. Individual Characteristics of Evidence.

Class Characteristics of Physical Evidence. Those characteristics shared by all members of a class of evidence Evidence cannot be identified to a single source Referred to as “class only” Examples are tire impressions, fibers from a garment, etc..

Individual Characteristics of Physical Evidence. Individual characteristics of an object when unique to a single source Called “individualization” Latent fingerprints are an example of individualized physical evidence When enough detail is present, tire impressions could also contain individual characteristics.

Class Only Characteristic Evidence. Drugs Fibers Hair Bloodstains (blood types) Glass Soil.

Class and Individual Characteristics. Fingerprints Fired bullets Toolmarks Bloodstains (DNA) Footwear impressions Handwriting.

Class: 38 caliber revolvers, 6 lands and grooves, right-hand twist Family: 38 caliber revolvers, 6 lands and grooves, right-hand twist Individual: Striated markings imparted to the bullet by the barrel interior.

Laboratory Analysis of Physical Evidence. The usual purpose is to individualize the physical evidence This process usually involves the comparison of the questioned item to a known item.

Comparative Analysis Process. First step is the comparison of the class characteristics of the questioned item to those of the known item If the class characteristics do not agree the known item can be eliminated If the class characteristics are found to agree and the questioned evidence has only class characteristics then it can be concluded that the known item is the source for the questioned item.

Results of the Comparison Process (1 of 6). When: Questioned item = Q Known item = K The questioned item has some similarities to the exemplar The questioned item has no similarity to the exemplar.

Results of the Comparison Process (2 of 6). 1. The class characteristics of the questioned item (Q) do not agree with those of the known item (K). Conclusion: (K) eliminated as the source of (Q)..

2. The class characteristics of (Q) agree with those of (K). Conclusion: If (Q) has only class characteristics, (K) may be the source of (Q)..

Results of the Comparison Process (4 of 6). 3. The class characteristics of (K) and (Q) agree, but there is no agreement in individual characteristics. Conclusion: (K) may not be the source of (Q) (inconsistent)..

Results of the Comparison Process (5 of 6). 4. The class characteristics of (K) and (Q) agree, and there is some agreement in individual characteristics between (Q) and (K). Conclusion: (K) may be the source of (Q) (consistent)..

5. There is sufficient agreement in class and individual characteristics between (Q) and (K) to establish that (K) is the source of (Q). Conclusion: (K) is identified as the source of (Q) (individualization)..

Comparison Standards and Controls. Questioned Comparison standards Reference standards Exemplar Controls.

Questioned. Refers to an item with an unknown source that is to be compared with a known source Other terms used to characterize the questioned item include: unknown, evidence, crime sample, latent.

Comparison Standards. Those materials collected from a known source for comparison with a questioned sample, in order to determine whether the questioned sample came from the same source as the comparison standard i.e., blood sample.

Reference Standards. Specimens kept in reference collection by the various labs They consist of specimens that have been collected from different sources and have been authenticated as to source and composition i.e., blood samples obtained from individuals of known blood types.

Exemplar. The term used to describe either a sample of the comparison standard that is collected or prepared from the comparison standard for the purposes of comparison with the questioned item It must be a true representation of the known sample to be useful in the comparison process.

Controls. Those items tested simultaneously with the questioned item to reveal any problems associated with the integrity of the evidence item or testing procedure.

Evidence Collection Requirements. Ethical Legal Scientific.

Ethical Requirements. The crime scene investigator must be objective with regard to the recognition, documentation, and collection of physical evidence at any scene It is the duty of the crime scene investigator to gather all relevant data regardless of the impact the facts may have on any theory of a case.

Legal Requirements for Evidence Collection. Search and seizure laws Documentation of the scene Identification of the physical evidence collected Chain of custody (Chain of possession).

Scientific Requirements. Preventing contamination of the evidence Preserving the condition of the evidence found Collection of adequate comparison standards.

QUESTIONS?.