As a Crime Scene Investigator and Bloodstain Pattern Analyst with over 36 years of experience, I have a talking point to discuss from last night's episode of CSI: Crime Scene Investigation.
When the CSI took the photographs of the bloodstains on the tennis court she was in a severe squatting position with the camera held at a steep angle in relation to the stains.
Take a piece of paper and draw a circle on it. View this circle from directly above it. It should look like a true circle. Now view it at an angle from the side. Distortion will make it appear to be oval, like an egg. The more severe the angle, the longer the appearance of the "circle". Since the ratio between the width and length of a bloodstain is a crucial element in its analysis, this distortion created through the camera angle is troublesome.
Therefore the photograph should have been taken with the camera directly over the stain - like a birds eye view flying over the scene. This position of the camera would help to eliminate distortion so that a circle looks like a circle. A passive drop of blood falling directly downward creates a circular stain but if there is direction (or elongation) to the stain that would indicate motion. Two very different scenerios in interpretatin to crime scene analysis
You may say that she was merely taking the photograph to establish the presence and location of the stains on the tennis court. I would counter that a close up of a dark stain on a gray background looks just like the other dark stains with a gray background and there is nothing to distinguish between the individual stains or anything to significantly establish their position relative to their location on the tennis court rendering this purpose useless.
One would need to step away and take a photograph with the location of the stain with something fixed and permanent in the background prior to taking the overhead closeup of the stain. This helps relate the stain location at a later time, usually in court.
And then there is the issue of taking a photograph of a fingerprint on a cylindrical clear bottle without a contrasting background or compensating for the curvature of the surface........
In case you missed it View CSI episode
Awesome. This is just one of the many reasons that I don't watch CSI (enter your favorite city here). I tend to pick it apart, saying things like "That's not how you do it" or "The opposing attorney would pick this investigation a part". I know that there is an expert on the staff who they consult with on the forensic matters. I can only hope this isn't a representation of his/her ability. Maybe the pose of her squatting was to emphasize her squatting rather than what she was doing.
ReplyDeleteI know these things. I was trained by the best.
J.D. Thomas