When the Evidence Speaks: Common Forensic Microscopy Techniques for Evidence Observation
Long before forensic microscopy techniques made their debut on TV drama and became familiar words even to high school students, it has always been in the forefront of modern forensic study and investigations. For one, forensic microscopy is one of the best tools with which to examine and analyze evidence, providing magnified images that show details that are otherwise difficult to see using the naked eye or an ordinary magnifying glass. Forensic microscopy is also not a method that uses only one optical microscopy technique for evidence observation. There are different microscopy techniques that may be utilized for just this purpose.
Firearm microscopy
This technique for evidence observation is one of the most commonly used where evidence includes guns and ammunition. Microscopical comparison is used to observe the striae or tool marks produced by a weapon when fired. This is an effective microscopy technique primarily because no two weapons will leave exactly the same striae on ammunition. Firearm microscopy allows crime scene investigators and police to determine whether a bullet entered as evidence was fired from a single weapon and if not, to trace which weapon used that bullet.
The forensic microscopy technique used for this purpose is the comparison microscopy, which allows side by side viewing of two images to check for similarities. The comparison microscope can show precise physical characteristics of two specimens and provide an image of the slightest differences in color, texture and structure. This type of forensic microscopy may also be applied to other trace evidence such as tool marks, hair, fiber and even documentation analysis.
Another forensic microscopy technique utilized in evidence observation that is related to firearm microscopy is the use of a scanning electron microscope. This type of optical microscope has one of the most powerful magnification capabilities of its kind, able to enlarge images of objects up to 100,000X. This microscope may be used to detect any gunpowder residue or particles that may be present on the hand or clothing of a suspect who might have recently used a gun. This type of evidence may be further confirmed with the use of chemical analysis to determine whether the same type of bullet found at a crime scene was used by the suspect.
Material microscopy
Evidence consists of many different things – wood, paper, plastic, fiber, metals, etc. – each of which exhibit different characteristics. This makes it necessary to use material microscopy for forensic evidence observation. A wealth of information based on the available evidence may be gathered using this microscopy technique. On metals, for example, any manmade scratches, damages, alterations, chemical reactions and manipulations will be readily observed using high magnification. This type of forensic microscopy technique also helps identify counterfeit documents by visual observation.
The forensic microscopy technique used for this type of evidence observation is performed with a metallographic or metallurgical microscope, which allows opaque objects to be viewed at high magnifications and in fine detail. Another type of forensic microscopy that may be effective with this type of evidence observation is the polarized light microscope. Although often used in petrology and geology, this microscope is also useful for viewing rock and mineral samples for analysis, allowing samples to be identified and their origin determined.
Another useful forensic microscopy technique is the transmission electron microscopy, often used to examine and analyze paint pigments. This will help determine the source and nature of trace evidence collected from a crime scene.
Fragment fracture matching microscopy
Many objects gathered from crime scenes and used as evidence are often found in less than perfect conditions. Some of them may have been torn, broken, split, fragmented or fractured whether by accident or deliberate force. Although they may seem like worthless pieces, this type of evidence is important for establishing a link among the perpetrator, the crime scene and the evidence itself. If a piece of material found in the crime scene is a matching piece to the material found in the possession of the perpetrator, an association can be formed.
Positive identifications may be established through the observation of the evidence, especially if the surfaces are refitted, matched or realigned and verified. Usually, this type of evidence is captured through the process of photomicrography to provide a hard copy for investigations and legal proceedings.
Live evidence microscopy
Not all evidence collected are inanimate objects. Some, such as blood and body fluids (saliva, semen, mucus, etc) may require special handling in order to be processed and accepted as evidence. In case these evidence need to be observed live or unstained, a dark field microscope may be used. This type of microscope allows specimens to be observed in their natural condition. For examination and analysis of bacteria culture, a tissue culture microscope may also be used to view specimens containing living tissue cultures.
