CSI And "Impressions"
CSI And "Impressions"
Richard Saferstein (Former Chief Forensic Scientist) gives expert video advice on: What are 'impressions' that are studied in CSI?; How does the study of tool marks help in CSI?; How are tool marks collected and analyzed in CSI? and more...
What are 'impressions' that are studied in CSI?
There are two types of 'impressions'. There are the impressions made, for example, of footsteps in dirt. That's a three-dimensional impression. There are also the types of impressions like when a dirty shoe comes into contact with a piece of paper. That's an imprint, and that's a two-dimensional impression.
How does the study of tool marks help in CSI?
Tool marks are important because they may contain individuality as a result of wear and tear. If a tool was pressed against a soft surface like wood or a lock, that tool may leave an impression of itself on that surface, and that impression may contain individualities that can be related back to the tool that was used to create the impression.
How are tool marks collected and analyzed in CSI?
That will depend on the location of the tool mark. What's best is to take the tool mark, in its entirety, back to the crime lab in its native state. However, often that can't be done. You can't remove windows and doors for that in any type of crime scenes. An impression will be made at such a crime scene, usually with silicon putty, and then the silicon putty impression will then be brought back to the crime laboratory for further analysis.
How does the study of footprints help in CSI?
The important thing about a footprint is the individuality that it contained. We have a general pattern associated with footwear that relates to its make, its size, its configuration and all of that. But that may not tell us exactly from what shoe the impression was made. The knowledge of the shoe, the exact shoe, comes from wear and tear markings that arise as a result of using that shoe and perhaps are present in an impression that is left at a crime scene and it's the search for those individual characteristics that are carried out in the crime lab.
How are footprints collected and analyzed in CSI?
The first thing one has to do is preserve the impression, and that's done through photography. Detailed photographs are taken at the crime scene of the impression. Second is to preserve the footprint through casting, and that is done either with plaster apparatus or dental stone. Once the photographs and the plaster impressions are brought back to the lab, the analyst will look for the general configuration or at the general configuration of the impression, it's size, it's shape, it's dimensions and all of that. What's most important is to look for individuality in the impression. Things that arise through wear and tear of the shoe. It's those individual characteristics that are compared to the shoe in question in order to make the ultimate comparison or identification of that suspect's shoe.
How does studying teeth impressions help in CSI?
Like any other impression, what we look for are individualities associated with the impression and in this case, teeth. Individualities that come about as a result of biological factors such as wear and tear that are associated with the use of the teeth. It is the collection of these factors, however, that must be looked at by a trained individual, and that trained individual is a Forensic Odontologist, who is specifically trained to carry out a comparison of teeth, with teeth impressions, for investigative purposes.
How are teeth impressions collected and analyzed in CSI?
The most important thing is to preserve the impression, and that must be done with photography. A forensic photographer will take detailed photos of the impression, and it will be those photos that will be analyzed back in the crime lab. Again, what is looked at are the individualities associated with the impression: the spaces between the teeth, wear and tear associated with the teeth, things of that nature. That can only be done by a trained forensic deontologist.