Forensic Science Errors and expert testimony

In this assignment you are an expert witness for the defense. Your job will be to use what you have learned about collecting and analyzing glass evidence to identify errors or possible weaknesses in the case presented by the prosecution.

You will evaluate the case presented by the prosecution in a glass evidence case. Your role is as an expert defense witness. Your task is to use what you have learned about glass evidence and analysis to find areas of weakness or errors in the case presented by the prosecution.

1. Read the body of evidence presented by the local crime lab (below). Identify at least 3 ways that the evidence presented could be explained to the jury as incorrect, unreliable, or incomplete due to an error in the collection or analysis, or what you have learned about the general reliability of glass evidence.


Prosecution Case Report 2.12 Glass Analysis

10/1 Glass Documentation and Collection at Crime Scene.

Glass fragments from broken window (on wall adjacent to bed) and broken glass lamp on opposite side of bed (laying on floor between bed and wall) photographed and then collected. Fragments collected by hand and stored in sealed bag (labeled “Glass Fragments from Bedroom”).

Glass fractures in window photographed. Three rings of radial fractures are evident from successive penetrations, with a hole in the middle of each radial fracture that is consistent with .38 ammunition.

Determination of force at the crime scene conducted. Based on the pattern of radial fractures, the first fracture was the bottom right, then left and then top right.

10/1 Glass Collection from Suspect in Custody

Asked suspect to remove clothing and place in labeled evidence bag. Bag labeled and sent to lab.

10/2 Analysis of Glass Collected from Suspect at Lab

Clothing removed and placed on surface. Items tugged, shaken, and scraped over collection surface. Dislodged glass from socks noted and removed.

Glass removed from sock and immediately examined under a microscope. A refractive index of 1.49 measured and documented. A plasma mass spectrometer analysis was then completed. Sample results matched to window pane of Type ClearVision with 99% accuracy.

10/5 Analysis of Crime Scene Glass at Lab

Removed glass fragments from labeled “Glass Fragments from Bedroom”. Cleaned and then crushed sample and then completed plasma mass spectrometer analysis with sample. Matched sample results with 100% accuracy to window pane Type ClearVision sold exclusively at Home Depot.

Attempted a fracture match reassembly of the broken lamp. Was unsuccessful due to mixture of fragments from window in collection.


2. Present your findings to the defense team. You may choose to make a presentation, such as a Power Point, write a summary and submit, or construct a diagram (you can use a tool such as (Links to an external site.)Links to an external site. if you choose) that correlates the evidence presented to an error.

3. Include the rubric below (copy and paste) in your presentation. Make sure to self-evaluate before submitting to ensure you have earned all the possible points. 🙂


Points Possible

Points Earned

3 Identified Errors or Sources of Unreliability


Explanation of Each Error / Point of Weakness using concepts from lesson


Organization and Clarity of Presentation


Total Points


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