Chapter 3 Physical Evidence

What is Physical Evidence? Physical Evidence defined Anything that may be found, by investigators, to have a connection with a crime any evidence introduced in a trial in the form of a physical object, intended to prove a fact in issue based on its demonstrable physical characteristics. Physical evidence can conceivably include all or part of any object.

Sometimes Evidence is divided into two types: Physical EvidenceBiological Evidence Physical evidence refers to any item that comes from a nonliving origin Ex: tire marks; footprints Biological evidence always originates from a living being Ex: DNA

Physical Evidence – Exchange Principle (Edmond Locard) This is evidence that does not forget. It is not confused by the excitement of the moment. It is not absent because human witnesses are. It is factual evidence. Physical evidence cannot be wrong, it cannot perjure itself, it cannot be wholly absent.

Physical Evidence vs. Eyewitness Testimony As such, loss of memory, confusion due to "the excitement of the moment," are real issues. Eyewitness testimony can, indeed, be wrong, either due to human error, or due to deliberate perjury. Eyewitness testimony may be "wholly absent," but even if it does exist, eyewitness testimony, just like a confession, is no longer enough in a court of law.

Physical Evidence In the late 19th century, up through the modern day, physical evidence has become the cornerstone of most criminal proceedings. It is important to understand that there are many types of evidence used in modern forensics. I say "modern" because changes in technology have greatly expanded the types of evidence available to the crime scene investigator. To borrow, once again, from Locard: "Not only his fingerprints or his footprints, but his hair, the fibers from his clothes, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen he deposits or collects."

Need for Microscopes Imagine a world without microscopes, and much of this evidence is not useful. Even the nature of an obvious form of evidence, blood, has changed dramatically over the course of the last 150 years. From Sherlock Holmes we know that old blood stains used to be indistinguishable from other stains:Sherlock Holmes "Are they blood stains, or rust stains, or fruit stains, or what are they?"

Types of Evidence Type:What to look for: Bodily Fluids: Blood, Semen, & Saliva – subject to serological analysis for determination of identity and possible origin Documents – any handwriting and typewriting submitted so authenticity or source can be determined Drugs – any substance seized in violation of laws regulating the sale, manufacture, distribution, and use of drugs Stains, dried stains, cigarette butts Type of paper, ink, typeface, burned/charred docs, obliterations, etc. Chemical identification is necessary

Types of Evidence Type:What to look for: Explosives – any device containing an explosive charge, as well as all objects removed from the scene of an explosion that are suspected to contain the residues of an explosive Fibers – any fiber whose transfer may be useful in establishing relationship between objects and/or persons Fingerprints – all prints of this nature Devices, residues, shrapnel, etc. Natural vs. Synthetic Visible or Latent, need to be photographed and lifted

Types of Evidence Type:What to look for: Firearms and Ammunition – any firearm, as well as discharged or intact ammunition, suspected of being involved in a criminal offense Glass – any glass particle or fragment that may have been transferred to a person or object involved in a crime. Hair – any hair present that could link a person with a crime Includes ballistic toolmarks Fragments, plus windows with serial fractures Animal vs. Human

Types of Evidence Type:What to look for: Impressions – Includes all forms of tracks Organs and Physiological Fluids – Body organs and fluids are submitted for toxicology to detect possible existence of drugs and poisons. Can also include blood for the presence of alcohol/drugs Paint – any paint, liquid or dried, that may have been transferred from the surface of one object to another during the commission of a crime Tire marks, footprints, fabric impressions, bite marks Chemical tests necessary Can be traced to a manufacturer

Types of Evidence Type:What to look for: Petroleum Products – gasoline residues removed from the scene of an arson, or grease and oil stains whose presence may suggest involvement in a crime Plastic Bags – a polyethylene disposable bag such as a garbage bag may be evidential in a homicide or drug case Plastic, Rubber, and Other Polymers – remnants of these man-made materials recovered at crime scenes may be linked to objects recovered in the possession of a suspect perpetrator. Residues Chemical tests necessary

Types of Evidence Type:What to look for: Powder Residues – any item suspected of containing firearm discharge residues Serial Numbers – includes all stolen property submitted to the laboratory for the restoration of erased id numbers Soil and Minerals – all items containing soil or minerals that could link a person or object to a particular location Residues On stolen property, or on weapons (may be detected if scraped off!)

Type of Evidence Type:What to look for: Tool Marks – includes any object suspected of containing the impression of another object that served as a tool in a crime. Vehicle Lights – examination of vehicle headlights and tailights is normally conducted to determine whether a light was on or off at the time of impact. Wood/Vegetative Matter – any fragments of wood, sawdust, shavings, or vegetative matter discovered on clothing, shoes, or tools that could link a person or object to a crime location Blunt objects/injury, screwdriver/broken locks, etc. Presence of fragments

Types of Evidence Type:What to look for: Injuries The type of injury, such as ligature marks, are crucial to understanding an assault or murder

Significance of Physical Evidence Identification – the process of determining a substance’s physical or chemical Identity to link a person to a crime Comparison - to find if multiple pieces of evidence have a common origin: Ballistics to determine if they were from the same gun Fingerprints of residents of a house need to be taken to determine which fingerprints are foreign Individual characteristics – properties of evidence that can be attributed to a common source with an extremely high degree of certainty matching ridge marks on fingerprints Class characteristics – properties of evidence that can only be associated with a group and never with a single source Race and gender Probability is used to determine the frequency of an event

Crime Scene Reconstruction All of this eventually leads to crime scene reconstructioncrime scene reconstruction The method used to support a likely sequence of events by the observation and evaluation of physical evidence, as well as statements made by those involved with the incidents.

Scientific Method Help distinguish evidence from coincidence without ambiguity. Allow alternative results to be ranked by some principle basic to the sciences applied. Allow for certainty considerations wherever appropriate through this ranking of relevant available alternatives Disallow hypotheses more extraordinary than the facts themselves. Pursue general impressions to the level of specific details. Pursue testing by breaking hypotheses (alternative explanations) into their smallest logical components, risking one part at a time. Allow tests either to prove or disprove alternative explanations (Hypotheses)