At the Lab: Hair & Fibre Analysis
Locard's principle of exchange states that every contact with another person or with an object leaves a trace. This means that at any crime scene there is evidence left behind that can help solve the case. This evidence can include hair and fibres.
Identifying Hair
- One type of trace evidence often found at a crime scene is hair.
- After hair is collected it is sent to the lab for analysis.
- Here a forensic chemist (FC) studies it under a microscope.
- The first thing the forensic chemist does is determine if the hair is from a human or an animal.
- If the hair is wider than 0.2 cm it is likely the outer hair, or guard, from a larger animal. If the hair is 0.2 cm or narrower, it could be human hair or hair from a smaller animal.
- If the medulla, or central core of the hair, measures more than 1/3 the total width of the hair, it is most likely an animal hair. If it is less than 1/3 the total width then it is probably a human hair.
- If the medulla has a ladder-like pattern it is an animal hair. If it has a continuous pattern with no ladders it is a human hair.
- If the scales on the hair have a variable pattern it is an animal hair.
- If the scales have a more symmetrical pattern (overlapping, like shingles on a roof) it is a human hair
- Once the forensic chemist has determined a hair comes from a human, he can study it for other information.
- Sometimes the race can be determined.
- If the hair is coarse, curly, and black and the medulla is broken then it could be from a person of African or African-American descent.
- If the hair is blonde and fine and the medulla is sparse, then the owner could be Caucasian.
- However, because many people are of mixed racial background, their hair cannot always be identified so easily.
The Real Value of Hair Evidence
- If a hair from a crime scene matches one retrieved from a suspect, it suggests the suspect was at the crime scene.
- However, it doesn't necessarily prove he committed the crime - only that he was there at some point.
- To compare two hair samples directly, the forensic scientist will use a comparison microscope.
- A comparison microscope has two stages and two eyepieces.
- When you look at them together through the eyepiece, you have a split screen, where half is the left side and half is the right side.
- This allows the forensic scientist to compare the samples on each slide.
- Scientists can also determine if the hair was forcibly removed or if the owner was taking prescription medication or even illegal drugs.
- Using a technique called neutron activation analysis, forensic scientists can analyze the chemical makeup of a substance, like hair, for important clues.
Did You Know?
- Napoleon Bonaparte was the Emperor of France in the early 1800s. Following his defeat at the Battle of Waterloo, Napoleon was banished to the island of St. Helena. He died there six years later.
- One hundred and forty years after his death, forensic toxicologists tested a lock of Napoleon's hair using neutron activation analysis.
- This test revealed that Napoleon had high levels of arsenic, a poison, in his body.
- Some people suggested that Napoleon had been poisoned to death.
- This idea was rejected when toxicologists found equally high levels of arsenic in many other people they tested.
- Their conclusion? People in the 19th century were exposed to naturally high levels of arsenic in the environment.
Fibres
- Often when a crime is committed, fibres are transferred from the suspect's clothing to the victim's clothing, and vice versa.
- If the identification officer finds fibres such as these at the crime scene, he or she will collect them using special adhesive tape.
- The identification officer will then send these fibres to a forensic chemist for analysis.
- FC uses a microscope to look for fibres on the victim's clothing that are the same colour as those on the victim's clothing.
- For example, if the suspect's shirt is red, the FC will look for red fibres on the tapings taken from the victim's shirt.
- If he finds any, the FC removes them very carefully using tweezers or forceps.
- He then places each red fibre on a separate glass slide.
- The FC then removes red fibres from the suspect's shirt and similarly mounts these on other glass slides.
- Next, the FC compares the fibres samples using a comparison microscope.
- This tool allows the FC to directly compare a red fibre sample from the victim's clothing with one taken from the suspect's clothing.
- If the two samples exhibit the same physical properties, the FC will do further testing.
Wayne Williams Case
- From 1979 to 1981, thirty young black males were murdered in the Atlanta, Georgia area. Police suspected a serial killer but at first had no real suspects. Eventually their attention turned to a 23-year-old local named Wayne Williams.
- With the help of forensic scientists, police were able to match fibres found on the victims with ones from the carpet in Williams' car and in his apartment. Williams' hair and his dog's hair were also found on several of the victims. Based on this evidence, Williams was convicted of the murders of two of the victims and sentenced to life in prison. He is believed to be responsible for the other murders as well.
Important Terminology
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