Physical Evidence

Physical Evidence: Learning Objectives Review the common types of physical evidence encountered at crime scenes Explain the differences between the identification and comparison of physical evidence Define and contrast individual and class characteristics of physical evidence Appreciate the value of class evidence as it relates to a criminal investigation List and explain the function of national databases available to forensic scientists

Physical Evidence: Vocabulary Class characteristics Comparison Identification Individual characteristics Product rule Rapid DNA

Amanda Knox: A Flawed Case of Murder September 2007 Amanda Knox moves to Italy as a foreign exchange student with the University of Foreigners Knox shares a cottage with 3 other women, including Meridith Krecher Within weeks of her arrival, Amanda becomes romantically linked to Raffaele Sollecito

Amanda Knox: A Flawed case of Murder November 1st, 2007—Meridith Krecher is brutally murdered Her naked body was found in her bedroom covered by a bedspread soaked in blood with stab wounds to her throat

Amanda Knox: A Flawed Case of Murder Police arrest and charge Rudy Guede, Amanda Knox, & Sollecito for the murder of Meridith Krecher Guede’s DNA had been found in several places in Krecher’s room Knox’s DNA had been found on the handle of a knife that had Krecher’s DNA on the blade The knife was found in Sollecito’s apartment Sollecito’s DNA was found on a bra clasp that belonged to Krecher

Amanda Knox: A Flawed Case of Murder On December 5th, 2009—Amanda Knox is sentenced to 25 years for faking a break in, sexual violence, and murder October 2011—Knox is acquitted January 2014—retrial; Knox found guilty March 2015—Knox is acquitted due to “glaring errors”, “investigative amnesia”, & “guilty omissions” https://www.youtube.com/watch?v=G5_MKlCJEd0

Common Types of Physical Evidence Blood, semen, saliva Documents Drugs Explosives Fibers Fingerprints Firearms & Ammunition Glass Hair Impressions Organs & Fluids Paint Petroleum products Plastic bags Plastic, rubber, polymers Powder residue Serial numbers Soil & minerals Tool marks Vehicle lights Wood & vegetation

The Examination of Physical Evidence: Identification Identification—process of determining a substance’s physical or chemical identity Crime lab could be asked to: Identify the chemical composition of drugs Identify gasoline in residue recovered from arson Identify the nature of explosive residues Identify blood, semen, hair, or wood for species origin

The Examination of Evidence: Identification Each type of evidence requires different tests—each test has its own degree of specificity Identification procedures: Determine tests needed for identification Eliminate all other possibilities

Individual Characteristics Evidence that can be associated with a common source possesses individual characteristics Properties of evidence that can be attributed to a common source with an extremely high degree of certainty Matching ridge characteristics of two fingerprints, striations (markings) on bullets or tool marks, handwriting characteristics, etc.

Class Characteristics Class characteristics are the properties of evidence that can be associated only with a group and never a single source EX. paint chips of a similar color can be traced back to a car model, but not a specific car

0.44% of people have that specific combination Product Rule The product rule states that multiplying together the frequency of each factor in the blood sample will determine how common blood containing that combination of factors is in the general population EX. Bloodstain found at the scene of the OJ Simpson case: Factors Frequency Type A 26% EsD 85% PGM 2+2- 2% 0.26 x 0.85 x 0.02 = 0.0044 x 100 = 0.44% of people have that specific combination

The Significance of Physical Evidence Forensic scientists must create and update databases for evaluating the significance of class physical evidence Most of the items recovered at the scene cannot be linked to a specific person The chances of finding class physical evidence is greater than physical evidence with individual characteristics The more evidence linking an individual to a crime, the more likely the individual was involved

Cautions & Limitations on Dealing with Physical Evidence Because of the image portrayed by TV and books, physical evidence is heavily weighted during jury deliberations Physical evidence may exonerate (exclude) a person from suspicion DEBATE: when does evidence cross the line between class and individual?

Forensic Databases Crime labs are on the forefront of the investigation seeking to identify the perpetrator Computerized databases link all 50 states & agencies around the world

Fingerprint Databases Integrated Automated Fingerprint Identification System (IAFIS) Launched in 1999 Fingerprints and corresponding criminal history information About 500 million fingerprint images

DNA Databases Combined DNA Index System (CODIS) Fully operational in 1998 Enables federal, state, and local crime labs to exchange and compare DNA profiles Rapid DNA—a process for developing DNA profiles from a buccal swab in 90 minutes or less that are compatible with a CODIS search TIME IS OF THE ESSENCE!

Other Databases National Integrated Ballistics Information Network (NIBIN) Compare markings made by a firearm on bullets & cartridge casings recovered from crime scenes International Forensic Automotive Paint Data Query (PDQ) Contains information about make, model, year, and assembly plant on more than 13,000 vehicles National Missing & Unidentified Persons System (NamUs) Missing Persons database, Unidentified Persons database, Unclaimed Persons database

The Examination of Evidence: Comparison Comparison is the process of determining whether two or more objects have a common origin A suspect may be placed at a location by noting similarities of a hair found at the crime scene to hairs from the suspect’s head 2 step process: Combinations of properties from suspect and reference samples for comparison are chosen Draw a conclusion about the origins of the specimens