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Volume III: Forensic Evidence at Murder Trials in Phoenix, Arizona

NCJ Number
Date Published
Tom McEwen, Edward Connors
Publication Type
Grant Report
This third volume of a three-volume report on a study of homicide investigations and case processing by the Phoenix Police Department (PPD) examines the impact of forensic evidence at murder trials, based on transcript reviews of 22 trials following arrests made during the 2 years of the Phoenix Homicide Clearance project, which consisted of transferring four crime-scene specialists from the crime lab to the department’s homicide unit for the purpose of collecting evidence at homicide scenes.
Eight trials included testimony by forensic scientists from the crime lab’s DNA section. Their testimony had a major impact in five of those trials. Testimony on DNA evidence is powerful because of the underlying science of DNA. Forensic scientists testified on ballistics analysis at 13 trials. This testimony had a major impact at five trials, moderate impact at two trials, and minor impact at six trials. Gunshot residue (GSR) analysis had a moderate impact at two trials, a minor impact at one trial, and no impact at four other trials. Latent fingerprint analysis and trace analysis had limited impact at the trials. Latent print examiners were called to testify in only three trials. Their testimony had no impact on the outcomes of these trials for two reasons. First, an outcome of “no match” was the result of many comparisons made between latent prints obtained from the crime scene against the fingerprints of suspects and victims in the case. Second, no probative value resulted from the matches that were found, because the matches were easily explained by the defense. Forensic scientists from the crime lab presented trace analysis at only two trials. In one trial, the testimony supported the testimony of a surviving victim, and in the second trial, the trace-evidence testimony supported the prosecutor’s theory of the case. 2 exhibits and appended summaries of case investigations and trials, forensic evidence collected and analyzed, and definitions of terms
Date Created: January 21, 2014