the Forensic Methodologies

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Trichology, or the scientific study of hair, is a discipline that began in the mid-1800s. Hair is obtained as forensic material at a crime scene and used for forensic analysis to provide crucial details needed to locate a suspect or victim. Forensic investigators perform various forms of hair examination and may say a lot of facts. Among the things analyzed include the DNA from the hair follicles, use of outlawed drugs and substances, presence of heavy metals in the body, the racial background, toxicology, age, and sex, whether there was violence during the suspect and victim, hair treatment and lastly the mineral deficiencies. The information can be useful in case there is paternity test, testing the use of drugs, medical reasons, assessing environmental pollution by heavy metals and when in the process of solving a crime (Girard, 2006).

DNA Information

The hair DNA from the hair follicle found at the root of the hair shaft. One hair can be able to provide enough information. Hair with a follicle structure has nuclear DNA ( nDNA) while a shaft without a root has mitochondrial DNA (mDNA).

Hair Toxicology

Hair toxicology information comes from a test that finds out if a person has ingested a poison intentionally or unintentionally, abused drug and substances or the exposure to different pollutants in an environment within5-90 day. The data may be obtained according to the dosage level or in the case of long term use. A good example of these drugs includes heroin in its metabolized form called the morphine stored in the hair follicle. Others include cannabis, cocaine, and amphetamine.

Racial Background

Race is the third information that can be retrieved from hair evidence although it’s challenging to assess head hairs of young children. The hair samples can be from three racial groups Asian, European and African. The features that used when identifying these ethnic groups are hair pigmentation or colour, texture, form, medullation and the hair cuticle (Sen 2010, p. 5).This information can be used to eliminate the suspects in an investigation based on the racial ancestry.

Age and Sex Identification

Age and sex are the fourth categories of the information that hair can provide in an inquiry. Although it is difficult, investigators can be able to differentiate the hair of an old person from that of an infant using the following aspects like the texture, loss of pigment or the colour of the hair. For the sex determination, the forensic scientist look for the length of hair since the majority of general women have long hair while men have short hair, women also have treated hair in most cases. The sex chromatin found in the cells at the base of the hair is also useful (Sen 2010, p. 6).

Forceful Removal and Treatment of Hair

This type of information is obtained through the physical examination of the hair using a light microscopy. Hair can be shed naturally or forcibly removed from its follicle. If the hair is from natural shedding, it has a ball-like root at the base while that of forceful removal is stretched and may have some tissue on it. Those muscles become valuable to the investigators to show whether there was violence between a suspect and the victim. Treatment of hair is also information that can be evident on hair. Hair dyes point out artificial treatment and their time of application shown by the length of the hair.
Another aspect that hair evidence can be used to identify is if an individual is suffering from mineral deficiencies.

Methods of Hair Analysis

When investigators arrive at a crime place, they collect any available evidence that a suspect might have left behind when in contact with the victim. Hair is gathered from the site of the crime and taken through several methods to come up with information that can help to identify the main suspect in a crime. A lot of care is taken during the collection of hair evidence to avoid contamination when transferring hair from one object to the other. Various hair treatments give useful information to the forensic experts including microscopy, chemical analysis for drugs and toxins (toxicology), DNA analysis or testing for the hair follicle.


Microscopy is the first method used to produce legal information by experts. It involves microscopy and macroscopy where different hair samples are viewed simultaneously using a particular type of a microscope for hair analysis called comparison microscope. The magnification used ranges from 40 times up to 400 times.The color, length, and curliness of the hair samples are the characteristics observed during the macroscopic process. The microscopic process involves observation of the following characteristics as cortex pigmentation, scales on the cuticle and the medulla pattern. Different microscopic methods are used during the microscopic process for example phase contrast microscopy, in this technique uses a unique objective lens, and condenser is used with a compound microscope to bring fine details into the structure of the hair(Moeller 1996, pp. 444-450).If hair has dye, forensic investigators carry out a fluorescence analysis where microscope filters are used to detect hair treatment and color. The electron microscope is the most efficient in the microscopy technique since it has a high magnifying power more than 50000 times for fine external and internal details of the hair.

Testing for Substances in the Hair Shaft (Toxicology)

Toxicology is the second major treatment that gives vital information about drug and substances in the body, poisoning, exposure to pollutants and other forms of toxins. Toxicology is possible because hair originates from the skin; this means that the chemicals that are taken by the skin are more likely to be found in the hair. Experts perform a chemical which can detect toxins like heavy metals like lead, drugs and other toxins. Toxicology uses different analysis methods including immunoassay, mass spectrometry, and the gas chromatography
The first toxicology test dissolving of hair in an organic solvent is the first step, after which the solvent breaks down the hair keratin which releases any chemical that might be in it.A forensic expert carries out chemical analysis on the solution for various substances. This analysis can give evidence of poisoning or drug abuse like heroin, cocaine, amphetamines.
If there is need to determine the exact time of poisoning or drug use, the experts use a procedure of the length and growth of the hair. A normal human hair is known to grow about 1.3cm per month. The length of the hair is determined from its root to its tip the sections where toxins and experts record. For example, if the toxins occur 8cm from the root, the estimated number of months since consumption of the drugs or exposure to the chemicals is 8cm divided by 1.3cm per months which gives approximately six months(Marie 2005 pp. 199-208).
The third technique under the toxicology method is the neutron activation analysis or NAA.This process involves putting the hair in a nuclear reactor, and high energy neutrons are used to attack it.Different gamma radiations with different signals give out various elements in the hair.Experts interpret those signals and determine the concentrations of various elements in that sample. The examples of elements identified through this analysis include zinc, manganese, sodium, bromine, argon, and antimony.

Testing the Hair Follicle Method

This is the third way in hair analysis. It gives the DNA information for sequencing from the hair follicle as well as identifying removal of hair by use of force or naturally shed from the body of a victim or a suspect.If there removal of hair by use of strength, it usually has a hair follicle at its base, and this refers to as the follicular tag. In that case, the hair may also contain some blood and other tissues at the hair follicle which forensic experts can use to determine victims or suspects blood group.

The second technique in the analysis of the hair follicle is the DNA analysis. Although this method is not fast and profitable, it is useful if microscopy information matches with that of a suspect. There are two types of DNA analysis done namely the mitochondrial DNA and nuclear DNA analysis. The mitochondrial DNA analysis is done to the hair without the telogen follicles since they lack cells that are nucleated. Those hairs have mitochondrial DNA in their roots and shafts. Hairs which have follicles have follicle tissue have cells which are nucleated. Those cells provide the nuclear DNA for analysis.

Value of Hair Evidence

The amount of hair evidence is weak compared to other types of forensic pieces of evidence like blood, and finger prints during investigations. Its value is affected by the method of collection at the crime scene, the analysis method used and forensic analyzers experience. The hair from the head and pubic regions are regarded more valuable than any other parts of the body. However, it has its unique values that make it reliable despite its difficulties in analyzing forensic information from it.

Easy to Document Time of Exposure to Substances

This is the first and the most significant value of using hair evidence. It is made possible by the fact that hair has a continuous growth and forensic experts can be able to determine the period of exposure to pollutants, use of drugs and poisoning. Forensics can identify the time of drug use by the help of the length of the hair as well as the growth rate of the hair. Experts can be able to document the period regarding weeks, months and years. In FBI investigations, hair evidence resorts if other information shows a drug abuse problem or if they want to eliminate multiple suspects in a crime.

The DNA Evidence

The DNA evidence obtained from the hair follicle particles and the hair shaft protein called the keratin serves as a core value in information. The DNA evidence is as reliable as they provide the necessary evidence that can be used to identify a suspected person or a victim of a crime. These two types of DNA are more reliable than the one obtained from other body evidence like saliva or blood.
Research has shown that it's possible to distinguish hairs of different people from each other and that gives a guarantee there can be no coincidence or accident in matching hair samples and if there is it's sporadic. Hair evidence becomes more valuable than other evidence when combined with other evidence, for example, a microscopy analysis can be strengthened by DNA confirmation (Douglas 2000 p. 3)


Hair evidence is the forensic evidence that forensic experts get at crime scene used by the investigator. It is a source of diverse information that led detectives to the suspect or a victim of a crime like rape, murder, and poisoning. These types of information include DNA, age, and sex, racial background, identifying if the hair comes out by force possibly during the suspects and victim contact, drug and substance abuse, exposure to pollutants like heavy metals. Experts can obtain this information through several methods of analysis like microscopy which uses light microscopy, DNA analysis using the hair protein keratin and the hair follicle, toxicology to help gain or any other chemicals and pollutants that might be present.
However, the hair evidence value is regarded useful if used together with other forensic information. It has great value because it can be able to expose how long an individual has been using drugs and other substance. Also, the DNA contained in the hair is of good value since it can be used to identify a suspect. The value has drawbacks as well because the hair is easily get contaminated besides being very difficult to obtain information from the hair. During the collection, the hair samples get mixed with other hairs that might be at the crime scene.


Douglas, W., 2000. Hair Evidence. Forensic science communication, Volume 2, p. 3.
Girard, J.E., 2006. Criminalistics: Forensic science and crime. Sudbury, Mass: Jones and Bartlett Publishers.
Linch, C.A., 1998. Evaluation of the human hair root for DNA typing after microscopic comparison. Journal of forensic sciences, 43, pp. 305-320.
Marie, B., 2005. Hair analysis for drugs of abuse. Biomed pap med, 149(2), pp. 199-209.
Moeller, R., 1996. Hair analysis as evidence in forensic cases. Therapeutic drug monitoring, 18(4), pp. 444-453.
Sen, J., 2010. Human hair in personal identification and documenting drug abuse. Anthropologist, 12(1), pp. 47-58.

May 04, 2022

Crime Science


Learning Genetics

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Forensic Science Study DNA

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