CSI PART 2: What a Scene!

23 January 2012

The scene of the show is set, the investigation is on, and, of course, Horatio is on the case. After examining the man's car, Horatio finds a number of clues, including dog hair on the car seat. This hair takes Horatio to a greyhound track and the case begins to unravel...

Horatio's murder investigation probably wouldn't have been successful if it wasn't for finding the dog hair, and rightfully so: Hair is one of the most common types of trace evidence found in a forensic investigation and can be very important for solving cases. The purpose of collecting hair is to determine where it came from: Is it from a suspect or the victim? Is it human or animal?

Did You Know?
Hair is commonly used in crime investigations both in TV and in real life Proof that cross-transfer of hair occurred between suspect and victim can be used to establish a physical connection between them. However, this only works in cases where the suspect and victim do not have legitimate reasons to be in contact. For example, if the offender is a family member who lives in the same place as the victim, the presence of their hair on the victim's body or clothing means nothing since the hair could easily have gotten there purely by chance.

If the hair is human, then an entire process of analysis begins to determine whether the person that hair is similar to that of the suspect.

Did You Know?
Hair is analyzed in two different ways: i) Whole hair analysis, and ii) Cross-sectional analysis Let's take a closer look at how it's done:

Whole Hair Analysis

A hair sample is analyzed as a whole and in cross-section. When viewed as a whole, the hair consists of 3 parts: the root, the shaft and the tip. Hair develops and grows out the skin from the hair follicle. Depending on the growth stage of the hair found on a victim, a follicle may be present. The follicle contains cells from the epidermis (i.e., skin) that encloses the root of the hair. Cells, as you know, contain DNA, so hair can be an excellent way to obtain DNA for analysis.

Did You Know?
Epidermal cells found on hair can be used as a source of DNA for genetic analysis

Did You Know?
Hair from different parts of the body have characteristic lengths and shapes, which can be diagnostic in a crime investigation The length and shape of the hair can also be used to determine the place on the body from where the hair came. These characteristics can then be compared to hair samples taken from the victim or suspect to see if there is a match.

(CRAM Note: for more on the biology of hair, see these articles in the Home-work section: "Hair to Dye For" and "Chemical Combat Against Acne")

Cross-Section Analysis

In cross-section, the hair consists of the cuticle, cortex and the medulla. The cuticle is the outer surface of the hair and consists of many scales, which are very specific to each species. It is important to remember that the best way to collect hair samples is with fingers (gloved of course) since hair is analyzed by observing these tiny scales and that the use of metal tweezers can destroy these fragile structures.

The cortex is the middle of the hair, which surrounds the innermost layer called the medulla. The medulla is a dark shaped structure that appears in different patterns according to the species of origin. In humans, the medulla may appear as a fragmented interruption of straight patterns, according to the racial origin of the donor.

Did You Know?
The medulla, which is the innermost layer of a shaft of hair, has characteristic patterns that can be used to determine the species and/or the racial origin of the donor Hair evidence can also tell an investigator whether the hair was pulled out or simply shed, and it can reveal whether the donor had dyed or permed hair. Since hair generally grows at a predictable rate of about 1 millimetre per day, investigators can even tell how long ago this hair treatment was done!

Did You Know?
Chemical treatments, such as dying or perms, can be determined from a single strand of hair, and can be useful information for identifying a victim or a suspect in a crime investigation

Did You Know?
Hair grows at a rate of 1 millimetre per day Hair is often present after the flesh and the rest of a body has degraded and disappeared. So, it can be used to test for poisons and medical conditions long after the rest of the body has disappeared. In fact, did you know that traces of arsenic (a poison) where found in the hair sample of Napoleon Bonaparte long after his death?!

So love him or hate him, Horatio knows what he's doing when he finds a piece of hair at a crime scene...and if it's like all the other episodes of CSI, it's the tiniest pieces of evidence like hair that can help break the case.

Katherine Steck-Flynn's interest in Forensic Science began when she worked as a special constable for the towns of Morinville and Beaumont in Alberta, Canada. She earned a Bachelor's degree in Anthropology from the University of Lethbridge, and also holds a certificate in Advance Specialty Health Studies, specializing in Forensic Science. She teaches seminars for law enforcement agencies in the areas of forensics and evidence collection, and is a staff writer for Crime Watch Canada. She has been a regular contributor to Law Enforcement Technology magazine and www.CrimeandClues.com and on occasion the Journal magazine and the U.S. Attorney General's Maine Law Officer's Bulletin. Her work is used for training by agencies in Ontario (OPP), Maine, North Carolina (North Caroline Dept. of Justice), Malaysia, China, and by New Scotland Yard.


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