How to Use Hairs as Evidence in Your Crime Fiction Novel

by | Sep 26, 2019

Hairs are a common type of forensic evidence. You want to use hairs as evidence in your crime fiction novel, and you need to make sure it’s right.

I’ve compiled a list of six things you should know to make sure your book is accurate.

Forensic hair comparisons are not routinely performed in crime labs today.

Forensic hair examinations cannot uniquely identify an individual. As a result, crime labs have moved away from these types of examinations and have focused on DNA.

In a nutshell, a typical forensic hair comparison consists of comparing a hair(s) from a crime scene to known reference hairs from a potential suspect or elimination sample (i.e., someone who also lived in the house).

Approximately 50 reference hairs are collected from five areas all over the scalp (both sides, top, bottom, and front). The examiner looks for distinguishing characteristics in the hairs to see if they are consistent.

Each lab is different in what they say about hairs

Crime labs differ in what they say about hairs in their notes/reports. At my old lab, we described the color, length, courseness, and the presence of a root in our case notes. We also stated whether the hair was human and suitable for DNA. Other labs might say the body region or type of animal (if non-human). It all depends on each lab’s policies.

Not all hairs are suitable for DNA analysis

Hair follicles go through three growth stages: telogen (resting), catagen (transition stage), and anagen (actively growing). Anagen hairs are the best type for DNA analysis. These hairs need to be forcibly pulled out of the head. Shed hairs found in a hairbrush or scattered around a room are most likely telogen hairs. If you use hairs in your book, it would be a good idea to have a struggle prior to the death of a person so that an actively growing hair that is suitable for DNA is pulled out.

Only one hair is needed for DNA

You don’t need a big chunk of hair to get DNA results. If multiple hairs are identified, only one is used for DNA analysis (depending on the case information). This is different than drug testing on hairs, which does require an actual lock of hair that is cut off near the base of the skull (roots aren’t required).

Where the hair is found matters

In criminal investigations, an item of evidence can have different meanings depending on where it’s found. This is known as its probative value. For example, a knife (murder weapon) used in a homicide is found near the body of the deceased (a woman). It’s tested for fingerprints, and the husband’s prints (the suspect) are found on the handle. Open and shut, right? Nope! The couple lives together. His prints would be on the handle of a knife in his own kitchen. In this situation, the fingerprints on the knife lose their probative value.

The same idea applies to hairs. In your books, you should focus on the relationship of the suspect to the victim. The closer the relationship, the less probative the hairs are to the investigation. If you’d like to use hairs in your book where the victim/suspect have a close relationship or live together, I’d place forcibly pulled hairs in the hands of the deceased and make sure it looks like there was a struggle (with defensive wounds).

Other forensic analysis options

There are two types of DNA in your cells. The type of forensic DNA analysis you’re most familiar with analyzes nuclear DNA. Nuclear DNA is found in the nucleus of a cell and is inherited from both of your parents.

Mitochondrial DNA is found in the mitochondria. It’s maternally inherited, and each cell has multiple copies. This type of DNA analysis is ideal for samples that are degraded or where nuclear DNA testing is not ideal. Your hair shafts no longer have cells with a nucleus (they’re made of a protein called keratin instead), so nuclear DNA testing is not an option. However, they do still have copies of mitochondrial DNA.

Mitochondrial DNA testing is not performed at traditional crime labs. This type of evidence has to be sent to a specialized lab for analysis. The FBI has four regional labs spread throughout the country that perform mitochondrial DNA analysis. Private labs will perform this type of testing for a fee.

There you have it! You are now officially ready to use hairs in your book! Do you have any other hair questions? Ask in the comments below!

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