The Quest for Confirmatory Data in Crime Scene Investigations

In today’s complex world a forensic chemist may prefer any physical evidence linking or exonerating a suspect from a crime scene to a false confession. This article utilizes forensic chemistry experimental approaches designed and implemented in an instructional workshop setting to present a unique perspective of certain facets of a crime scene investigation. An incident from a staged crime scene was investigated and physical evidence were collected, processed, and analyzed. The authors used modern techniques available in the field to analyze evidence recovered from the crime scene and the results were used to establish a link to one of three suspects. In our previous article [1], physical evidence collection, handling, analysis and evaluation were reviewed, as were challenges associated with carrying out these tasks. The information was presented in a way that may be beneficial to instructors looking to create or update existing forensic science courses, or scholars interested in the drawbacks of certain aspects of evidence collection. This article presents the experimental data generated from the analysis of physical evidence collected at the crime scene. The results can be classified as either presumptive or confirmatory. Some of the evidence recovered and analyzed such as fingerprints, bullets and casings, drugs, and DNA were shown to possess individual characteristics and when properly processed and analyzed can be used to exonerate or convict a suspect. Analysis of physical evidence with two methods Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) classified as confirmatory test instruments in forensic analysis is also presented. The GC-MS data presented, illustrates cocaine separations and identification in one analysis, and FTIR data illustrates identification of functional groups in fabric and cocaine. This information can be used by instructors to fully explain to students the science behind the techniques of GC-MS and FTIR as they relates to confirmatory identification. We have presented the information in a way that may help students identify the differences between presumptive and confirmatory tests as well as individual and class characteristics.