FIBERS

Cross Transfer

• happens when there is person to person contact
• can connect people to crime scenes if the fiber can be identified
• difficult because fibers are not unique and cannot definitively pinpoint an offender to crime
• there must be other factors involved such as evidence correlating to fibers or something that sets them apart

OHIO CASE

• 1982- kristen Harrison abducted from ball field in Ohio
• Body found 6 days later- raped and strangled
• orange fibers in hair looked similar to those found on 12-year old female murder victim in same county
• Their polyester make and trilobal shape allowed scientists to conclude that they were carpet fibers
• plastics wrap around her feet indicated that the killer once ordered a special van seat

Years Later...

• 28 year old women abducted, held prisoner, and tortured
• she escaped and reported him police found his van was similar to the one Kristen was in
• had orange carpet that matched the fibers in her hair
• unique color allowed scientists to trace it to manufacturer
• found that only a limited supply of this carpet sent to ohio, narrowing down possibilities

Analysis

• gathered at scene with tweezers, tape, or a vacuum then determined to be natural, manufactured or both
• natural fibers: plants or animals manufactured: synthetics (rayon, acetate, and polyester)
• analysts generally get only a limited numbber of fibers to work with- sometimes only one
• all collected fibers from crime scene are compared against fibers from a suspect source (such as car or home)
• fibers visually inspected through a microscope

MICROSCOPES

• Compound: uses light reflected from a source and magnified through lense
• Comparison: two compound microscopes joined by an optical bridge) used for more precise measurement
• phase-contrast: reveals some of structures of fiber, light beams pass through the structure for a magnified image
• scanning electron: converts emitted electrons into a photographic image for display

SPECTROMETER

• separates light into component wavelengths
• by passing light through something to produce a spectrum, resulting "absorption lines" can be read
• absorption lines: wavelengths that are absorbed into the substance are characteristic of its components
• then, a "spectrophotometer" measures the light intensities which yields a way to identify different substances

MICRO-SPECHTROPHOTOMETER

• locates minute traces or shows how light interacts with material under analysis
• increases accuracy when linked to a computerized spechtrometer
• scientist can get both a magnified visual and an infrared pattern at the same time

ANALYSIS: steps

• compare color and diameter
• dyes can be analyzed with chromatography to separate the chemical constituents
• chemical composition
• microscopic appearance- analyst looks for lengthwise striations or pits on surface

Case studies

• trace fibers are often thrown out in court because inaccurate
• claim they can be carried by anyone, making infinite suspect pool