Thursday, August 11, 2011

Forensic Investigation Of Glass Evidence


When analyzing glass fragments found on a suspect first you must find the source of where the glass fragments came from. If you can identify where the glass came from then you can find the area that the glass was broken. The First Response Officer should always make sure to draw a sketch of the crime scene depicting the place that the suspect was located at the beginning of the crime following a path to where the suspect ended the crime.  All items touched by the suspect are to be analyzed and photographed by the Forensics Investigator such items are to be   processed for fingerprints, shoe prints, DNA, and other analysis tests. Photographs have to be taken of the crime scene starting from outside to inside. Photographs are to be taken at general range, midrange, and close up; photographs have to be labelled distinctly listed by place on the sketch, time, date, and f stop.
The clothing items should be dried in the case they are blood stained and placed in a properly labelled paper bag or box.  The glass fragments left on the crime scene should be properly labelled and placed inside of a separate bag.  After putting the chain of custody on all items, the Forensic Investigator can then send them to the laboratory for further analysis. Glass fragments can also be stored in metal pill boxes as long as they are safely handled and labelled properly.
Check the window area for hair, blood, fingerprints and shoe prints this is an essential part of the investigative work.  Finger prints can be found by using a number of different methods some of the more prevalent methods include dusting with amino black, Ninhydrin, Superglue Fusing, and the use of silver nitrate to find latent fingerprints on metal surfaces such as window frames and door frames silver nitrate allow for clear fingerprint analysis of metallic items. 
Using a precipitin test to identify human blood then sending the blood samples into the laboratory for further analysis such as DNA and laboratory comparison. Shoe prints can be analysed by using a static lift kit if located on dry hardened floor surface or by a dental cast of the foot print if located in soft or semi hard mud or dirt.
A laser can be used to project the direction of the projectile that moved through the glass object, if you think the suspect has shot the window with a gun or had thrown an object through the windows a laser will tell the direction of travel of the object that has moved through the broken glass the Forensic Investigator may find linking evidence where the object may have been left after the crime occurred.
The use of a Hot Stage Microscope will determine the refractive index of the glass particles and diameter. The GRIM 3 identifies the refraction match points allowing the Forensic Investigator to find the exact matches of broken glass fragments.
If the object is subjected to a radial fracture this will mean that the whole was made by a moving object and needs to be processed at the laboratory for more information to identify a matching source of the concentric fractures to the glass found on the suspect.
The individual class characteristics include irregular broken glass objects that can only be associated with the window the suspect had broken. Other individual characteristics include blood, fingerprints, shoe prints and random striation markings on bullets and tools.  An example of individual characteristics is a cipher shaped piece of glass that fits to another piece of glass that is c shaped with both glass fragments having the same refractive index and refractive match points provided by GRIM3.
Blood is always a good place to start with analysis for a crime scene that involves sharp objects such as broken glass, knifes, splintered wood, and tool like objects. If you can get blood samples from the glass on the floor, on the suspects clothing, in or around the area of the crime will prove the suspect guilty.
Hair is practically a give me on the crime scene if the Forensic Investigator is able to find broken hair follicles along the floor or among the area of a broken window this evidence can be processed for DNA making a comparison of the DNA profile.
Skin is a body organ that is very likely to have an exact match for DNA. A swab of the suspect may match skin or other DNA found on the crime scene.
Class Characteristics are characteristics that lead to an uncertain observation of testing that usually makes a negative laboratory result.  Class Characteristics are usually hard to acknowledge they do not identify individual traits that lead to a suspect.
Examples of Class Characteristics include such items as fibers found on the crime scene that have no relation to the witness nor the suspect of the crime, hairs that were found that belonged to a house owners pet after the house had been robed, give no leads to what the suspect was looking to steal because the hairs do not belong to the suspect. Other items that may be considered class characteristics include glass fragments that come from a former window that was broken and reinstalled, broken glass bottle on the ground of an accident scene that was left before the accident occurred.
Interesting enough common views of crime scenes that involve broken glass by extensive research either have to deal with vandalism, assault, robbery or a vehicle accident. Most often a criminal will break glass when trying to enter a place to steal merchandise; a suspect would break glass to steal merchandise from a residential home or a business building thus breaking and entering.  Vandalism can be a factor a person may throw an object at a glass window for a spur of the moment thrill ride. During a fight that involves a struggle a glass object could be broken.  Other crime scenes that would have broken glass involved are accident scenes that the window glass or light covers have been damaged and or shattered.
 References                                                     

Fisher, Berry A. (2004) CRC Press, Techniques of Crime Scene Investigation

Saferstein Richard (2007) Pearson Prentice Hall, Criminalistics, An Introduction To Forensic Science Tenth Edition  













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