Fibers notes190920235.ppt
- 1. Fibers “Wherever he steps, whatever he touches, whatever he leaves even unconsciously, will serve as silent witness against him. Not only his fingerprints or his footprints, but his hair, the fibers from his clothes, the glass he breaks, the tool marks he leaves, the paint he scratches, the blood or semen he deposits or collects— all of these and more bear mute witness against him. This is evidence that does not forget.” —Paul L. Kirk (1902 – 1970) -Forensic scientist
- 2. Chapter 6 Satin Weave The yarn interlacing is not uniform Creates long floats Interlacing weave passes over four or more yarns Satin is the most obvious example
- 3. Chapter 6 Filament Cross-Sections Synthetic fibers are forced out of a nozzle when they are hot, and then they are woven. The holes of the nozzle are not necessarily round; therefore, the fiber filament may have a unique shape in cross-section.
- 4. Chapter 6 Testing for Identification Microscopic observation Burning—observation of how a fiber burns, the odor, color of flame, smoke and the appearance of the residue Thermal decomposition—gently heating to break down the fiber to the basic monomers Chemical tests—solubility and decomposition
- 5. Chapter 6 Testing for Identification Density—mass of object divided by the volume of the object Refractive Index—measuring the bending of light as it passes from air into a solid or liquid Fluorescence—used for comparing fibers as well as spotting fibers for collection
- 6. Chapter 6 Dyes Components that make up dyes can be separated and matched to an unknown. There are more than 7000 different dye formulations. Chromatography is used to separate dyes for comparative analysis. The way a fabric accepts a particular dye may also be used to identify and compare samples.
- 7. Chapter 6 Identification and Comparison of Fibers Fourier Transform Infrared analysis (FTIR)—based on selective absorption of wavelengths of light Optical microscopy—uses polarizing light and comparison microscopes Pyrolysis gas chromatography-mass spectrometry (PGC-MS)—burns a sample under controlled conditions, separates and analyzes each combustion product
- 8. Chapter 6 Collection of Fiber Evidence Bag clothing items individually in paper bags. Make sure that different items are not placed on the same surface before being bagged. Make tape lifts of exposed skin areas of bodies and any inanimate objects Removed fibers should be folded into a small sheet of paper and stored in a paper bag.
- 9. Chapter 6 Fiber Evidence Fibers are used in forensic science to create a link between crime and suspect. Direct transfer - fibers may be transferred directly from victim to suspect or suspect to victim. Secondary transfer - If a victim has fibers on his person that he picked up and then transferred to a suspect
- 10. Chapter 6 Fiber Evidence Fiber evidence in court cases can be used to connect the suspect to the victim or to the crime scene. In the case of Wayne Williams, fibers weighed heavily on the outcome of the case. Williams was convicted in 1982 based on carpet fibers that were found in his home, car and on several murder victims.