Forensic+Techniques

=Forensic Techniques =

__ ** Saliva on DNA Stamps and Envelopes ** __

Detecting DNA evidence at a crime scene involves the collection of any objects that could have made contact with a suspect's body. Sweat, blood, skin cells, or in the case of the Unabomber, saliva on stamps and envelopes that could potentially contain DNA. A forensic examiner must detect this DNA, duplicate, unwind, and identify the repeating codes of letters (called tandem repeats) which exist within the DNA. Identifying various combinations of repeats in letter's and spaces allows for comparison with other DNA samples and the repeats which were found in them. Depending on whether the repeating codes are the same or different, it can be determined if the DNA originated from the same source. This is assuming that the sample of DNA left behind was that of the nucleus of a cell, which allows for DNA indetification of an individual person. If the DNA does not include that of the nucleus, one can not necessarily be individually identified, but can be narrowed down to family members linked to the same maternal linkage (Saferstein, 2009).



__ **Typewriters** __

In order to determine the make and model of a typewriter that was used to prepare a document, the forensic examiner compares character style, shape and size. The typewriter will also be examined for wear and damage because these changes occur randomly and irregularly creating individual characteristics. Associating a particular typewriter with a typewritten document requires comparing questioned documents to documents made as examples prepared from the suspect typewriter. The examples must be typed word-for-word for proper comparison (Saferstein, 2009).



__ ** Writing Style/Handwriting ** __

Detecting this evidence involves the collection of written documents at a crime, whether written with intent to be read by the targeted individual or police, or any unintentional writing that could have taken place at the scene. A document examiner compares a document in question with one known to be written by a potential suspect. Ideally, a variety of documents from the suspect are compared, because although writing style is unique to each individual, variations can still occur in an individual’s writing; it will not be identical at all times. The examiner looks at many factors including angularity, slope, speed, pressure, and space between letters and words, size of letters, connected letters. A great deal of these factors must correspond in order for a determination can be made as to whether the handwriting is a match (Saferstein, 2009).



__ ** Ink Comparison ** __

To compare ink samples, they must first be removed from the paper/surface using a hypodermic needle to punch out small samples from the writing. Ink comparison can be done by first using thin-layer chromatography to separate the components of the ink. The sample is placed on a special plate and closed into a liquid-filled chamber. The liquid will rise up, causing the various components of a substance to separate and rise to different heights on the chamber wall. Thin-layer chromatography is used with ink evidence because it requires a very minimal amount of material to work with. Once these components have been separated, a visible micro-spectrophotometer is used to definitively identify specific materials that exist within the substance in question. The visible micro-spectrometer shines a beam of light into the material in order to determine how much of the light will be absorbed. Determining the absorption spectrum of a substance allows the forensic examiner to compare this to the known absorption rates of a wide variety of substances to conclude which one it is. Identifying the components of an ink mixture can allow ink to be attributed to a specific manufacturer, often in a specific year as well (Saferstein, 2009).



__ ** Paper Comparison ** __

Initial comparison can be done through appearance, colour, weight, and watermarks. Thorough comparison is done through fibre identification and characterization of additives, fillers, and pigments present in the paper. Initial examination of colour and watermarks can be visually compared through the use of a comparison microscope (Saferstein, 2009). To identify the fibres present in the paper for comparison purposes, thin-layer chromatography is used to separate components of the paper fibre, with a visible micro-spectrophotometer to identify specific fibre types (see ink identification for procedure details).



__ ** Fingerprints ** __

Detecting fingerprints at a crime scene depends on whether they are visible or latent. Visible fingerprints are apparent to the naked eye, left with a coloured substance that came into contact with the finger tips. Latent fingerprints must be detected using powders or chemical enhancement. Powders made from aluminum or charcoal may be used to create a contrast between the fingerprint and surface, or fluorescent powders may be used to make the fingerprints visible under UV light. This technique could be used to detect fingerprints on letters, wood or other porous surfaces suspected to contain prints from the Unabomber. Chemicals such as Ninhydrin could also have been used to create visibility of prints on porous surfaces. For testing prints on non-porous surfaces, such as the metal piping using to encase the bombs in this case, chemical enhancement such as cyanoacrylate would likely be used to create visibility of the prints through fuming glue that will attach to their shape. Laser light can also be used on a variety of surfaces to create visibility in prints, through the reaction between the laser and the perspiration which created the fingerprints. A forensic analyst specializing in fingerprints would then examine the visible prints and use a coding system to classify and score the prints through numbers assigned to various forms of loops, arches and whorls (Saferstein, 2009).



__ ** Materials Used to Make the Bombs ** __

Detecting explosive materials for forensic examination involves collection of all loose soil and debris surrounding the explosion using wire-mesh screens, as well as objects present close to where the explosion took place, as traces of the materials could have attached themselves to these objects. All of these materials should be stored in air-tight, metal containers. To determine and separate the types of explosive materials used in pipe-bombs, such as those created by the Unabomber, a forensic examiner would used an Ion Mobility Microspectrometer. This device vacuums suspected explosive materials into it, and applies heat and light beams to them. The speed at which they travel through the tube following this application allows examiners to distinguish the explosive material types involved. An infrared spectrophotometer may then be used to definitively identify the materials present through analysis of absorption of infrared light and a comparison of known absorption rates of materials. Alternatively, X-ray diffraction may also be used, which involves applying X-ray radiation to the substances and analyzing the diffraction pattern that is created when this radiation light bounces off. If the diffraction pattern produces an identical pattern to that of a known substance, the substance has been identified (Saferstein, 2009).



__ ** Wood (from cabin compared to wooden boxes holding the bombs) ** __

Wood used to make the box which encased the bombs planted by the Unabomber can be compared to wood from the cabin using a comparison microscope. This would allow for distinction between colour and type of wood. The edge at which the wood had been cut would also be compared under a comparison microscope with a cut or missing area of wood present in the cabin, to see if the cuts and splinters on each edge would match up to create what was once an entire whole piece of wood.