1. Tool Marks

2. What are tool marks? What are tool marks? How can tool marks help make a case? How can tool marks help make a case? If you and I own identical pry bars, how can a forensic scientist identify which one was used at a crime scene? If you and I own identical pry bars, how can a forensic scientist identify which one was used at a crime scene?

3. Tool Marks Tools make specific marks when they cut or scrape a softer surface Compression tool mark: shows outline of tool (hammer into wood) Sliding tool mark: parallel striations when tool slides across material (screwdriver or crowbar) Cutting tool mark: striations when tool cuts through material (scissors)

4. 2 Types of Characteristics 1.Class characteristics 1.Common to a group of objects 2.Example: A hammer has a distinctive shape and size. 2.Individual characteristics 1.Unique to a given object 2.Causes? 3.Example: shoes

5. Types of Tool Mark Impressions 1.Static (“impressed”) marks – Caused by a harder object being pressed into another softer object – Example: crow bar into wood 2.Dynamic (“striated”) marks – Caused when a tool slides or scratches across another surface – Example: sliding a key along the side of a car (Locard?)

6. Types of Tool Mark Impressions, cont… 3.Cutting (“crushed”) marks – Caused by pressure being applied to both sides of an object – Examples: pliers or wire cutters 4.Multi-stroke marks – Caused by repetitive actions – Example: a saw moving back and forth

7. Collection of Tool Marks  Notes, sketches, photographs  If possible, the tool mark should be taken back to the lab.  If not, a cast should be made. Silicone rubber ideal material

8. Collecting Tool Mark Evidence What do you think the FIRST step would be? What do you think the FIRST step would be? 2 nd step: 2 nd step: – Bagged and taken to lab for further analysis, if possible – Make a cast of the marks, usually with silicone rubber. What do you do with a recovered, suspect tool? What do you do with a recovered, suspect tool?

9. Examination of a Suspect Tool Step 1: ? Step 1: ? Step 2: ? Step 2: ? Make test marks with the tool. Make test marks with the tool. What piece of equipment would you use to compare the marks made in the lab with the marks made at the scene? What piece of equipment would you use to compare the marks made in the lab with the marks made at the scene? What other evidence can be obtained from a suspect tool? What other evidence can be obtained from a suspect tool?

10. Conclusions of analysis  If class characteristics and striations match, can say the tool mark was likely made by the suspect.  If class characteristics (and striations) do not match, the suspect tool can be excluded.  If class characteristics match but striations do not, the results are inconclusive.

11. Case Study Leah and Milton Rosenthal: http://www.channel4.com/science/micr osites/S/science/society/forensic_marks. html Leah and Milton Rosenthal: http://www.channel4.com/science/micr osites/S/science/society/forensic_marks. html http://www.channel4.com/science/micr osites/S/science/society/forensic_marks. html http://www.channel4.com/science/micr osites/S/science/society/forensic_marks. html The Lindbergh Kidnapping The Lindbergh Kidnapping