Trace Evidence


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Chemical Properties of Hair

Each strand of hair is made up of the medulla, cortex, and cuticle.

The innermost region, the medulla, is not always present and is an open, unstructured region.

The highly structural and organized cortex, or middle layer of the hair, is the primary source of mechanical strength and water uptake.

Melanin degradation is encouraged and sun linked decoloration intensifies.

Keratin itself is altered, making the hair fragile and easily damaged.

The organisation of keratin within its cortex allows it to resist a strain of up to about a hundred grams.

Physical Properties of Hair

Texture-Much of the attraction of a beautiful head of hair lies in its texture, or feel. The texture of hair depends on several things.

The first is the average diameter of the individual hairs. We have seen that these vary widely. The larger the hair diameter, the coarser it will feel.

Secondly, different people's hair naturally feels different: some hard and others soft, some silky and others wiry. The reasons underlying these differences are still a matter for scientists to argue over.

Thirdly, the texture is affected by the degree of weathering of the hair.

Finally, hair texture is affected by what has been put on it. Repeated lavish applications of hair spray gives hair a different feel from that of hair that has been freshly washed and conditioned. Conditioners make hair feel soft and smooth. Conditioners that contain silicones even give a slightly different feel from those that don't (most manufacturers do put silicones into conditioners nowadays, however, as they protect the hair cuticle). Contrary to popular belief, this altered feel is not a sign of build-up.


This is one of the most important properties of hair. Because of its elasticity, hair can resist forces that could change its shape, its volume or its length. Its elasticity lets it spring back to its original form without damage.

When healthy hair is wetted and stretched, it can increase in length by up to 30% and still return to its original length when it is dried. Stretching it more than this will tend to damage it, however, leading to permanent lengthening and even breaking.

The elasticity of hair depends on the long keratin fibres in the cortex. Chemical treatments of hair such as perming and bleaching can alter the cortex after repeated damage, and change the hair's elasticity. Hair with poor elasticity will stretch only to a limited extent. It will not curl, it will break easily when it is groomed and it cannot be permed satisfactorily.

Both natural sunlight and artificial ultraviolet light break down chemicals in the hair and damage its elasticity in the same way that bleaching does, though to a much lesser degree.


The moisture content of hair is greater when the atmosphere is moist and humid, and less when the air is dry. The reason why hair 'collapses' in hot, humid atmospheres is summed up by:

heat and humidity -> more moisture
-> less static electricity
-> collapse
In dry conditions:
heat and dryness -> less moisture
-> more static electricity
-> more volume (body)

Drug Testing w/Hair Analysis by Psychemedics: Drug Testing Company

Hair Case Study

Caught By A Hair

Case study

In 1990 in Telluride, Colorado, Eva Shoen's young daughter found her dead from a single gunshot to her head. Her husband, Sam, came under suspicion, but he truly appeared to be the grieving, shocked husband, a victim of random violence. The police were confident they would solve the case, because the bullet taken from Eva's skull had the distinct markings of a particular type of pistol. However, the case eventually found its way into the cold cases file. There just were no leads.

Three years later, the Telluride police received a call from a man in Arizona who believed that his own brother, Frank Marquis, had been the perpetrator. Marquis had once confessed this crime, but an attempt to trap him during a phone conversation failed. Nevertheless, when the gun was recovered, an arrest seemed a sure thing. Unfortunately, Marquis had covered his tracks all too wellincluding tampering with the barrel of the gun so that the bullet fired from it could not be matched. All they had on him was a hearsay conversation.

However, tracing Marquis's movements indicated that he had indeed been in Telluride during that weekend for a festival, and that he had a police record for rape. This was the man, the detectives felt, and they had to find a way to get him. Putting pressure on Marquis' travel companion, they learned that at some point along the road back, Marquis had tossed two bundles out the window of the car. They suspected that this was the clothing he had worn to commit the crime. Still, it was a long and winding road between Telluride and the point where Marquis had ended his journey some four hundred miles away.

Detectives scoured the roadway until they narrowed the possibilities down to four places. As luck had it, a construction crew had recently moved a pile of dirt, exposing a bundle of clothing that the dirt had preserved. On the shirt was a single strand of hair, which was examined in the lab against a sample taken from Eva Shoen. Forensic trace expert Joseph Snyder analyzed the color and structure, and pronounced them a close match.

When the investigators told Marquis of their findings, he confessed. It was a bungled burglary, he said, indicating his knowledge of the plea-bargaining system. Although the officers in charge of the case believed that he had in fact planned to rape Eva Shoen and had killed her in the process, they knew that this would be impossible to prove. Marquis got a sentence of twenty-four years for manslaughter.

Sometimes a single strand of hair will make all the difference between a case closing down and a lead that opens it in an entirely new direction.