Hair is also in contact with chemicals in shampoos, and any dyes, gels, sprays or other cosmetics that may be placed on the hair (11).
Since there is no standardized method for cleaning these external contaminants off of the hair prior to analysis, the potential for inaccurate results from external contamination is widespread. There is no way to tell in the laboratory if a chemical is contained within the hair, and therefore came from with in the body, or if it is on the surface of the hair and did not come from within the body (12). An enormous amount of scientific research studies have indicated that hair analysis is unreliable as a diagnostic tool in crime solving. For example, in one study, the researchers took hair from the head of a single individual and sent portions of the sample to six laboratories; the results varied widely from laboratory to laboratory (13). In another report released by the U.S. Agency for Toxic Substances and Disease Registry (ATSDR), the ATSDR concluded that for most substances, the presence of a substance in hair may indicate both internal and external exposure, but such exposure did not necessarily indicate the source of exposure. Additionally, this report also criticized the lack of standard procedures for sample collection, the lack of standardization of methods and quality assurance/quality control among laboratories, and the possible over-interpretation of results far beyond the current body of scientific data and in light of limitations of techniques and procedures (14). These reports indicated early on the need for a more suitable method of hair testing in addition to the traditional microscopic methods.
Historically, the early 20th century saw the birth of forensic science as a specialized profession, with laboratories and experts who aimed to link suspects definitively to crime scenes. Eventually, handwriting, fingerprints, photographs and blood samples became regularly introduced into evidence, and the belief that "every criminal leaves a trace" became a cornerstone of police investigations (15). By the late 1980s, DNA testing had been widely adopted, and currently has assisted in reversing guilty verdicts of innocent individuals. Just within the past few years, the rise of DNA testing has revealed enormous failings in the microscopic hair analysis that was considered reliable a generation ago. The use of forensic DNA analysis in solving crime is proving to be as revolutionary as the introduction of fingerprint evidence in court more than a century ago. Police and detectives have been using forensic DNA evidence for little more than a decade, however, it has emerged as one of the most powerful tools available to law enforcement agencies for the administration of justice. DNA analysis has been labeled as the next generation of human identification in the science of police investigations and is considered a major enhancement for the safety of all individuals. The scientific underpinnings of DNA analysis are well-tested and conceded to be solid even by critics (16).
The value of DNA to police investigations is enormous. Biological samples collected from a crime scene can either link a suspect to the scene, or rule the suspect out as the donor of the DNA. Evidence from different crime scenes can be compared to link the same perpetrator to multiple offenses, whether the crimes took place locally, across the country, or halfway around the world. Additionally, DNA can also identify a victim through DNA from close relatives. Using modern technology, DNA can be extracted from a small biological sample, such as a few drops of blood. This sample can be analyzed, creating a DNA profile that can be used to identify the individual the blood came from. Next, a DNA profile, drawn from a known biological sample, can be compared to an unknown DNA profile drawn from a different biological sample.
Nuclear and mitochondrial DNA analysis is a lengthy process that can be summarized simply. In a human cell, nuclear DNA analysis is extracted from inside the nucleus. There are two copies of Nuclear DNA in each cell, one that is received from an individual's mother and one that is received from their father (17). Outside the nucleus are small structures known as mitochondria, which have their own DNA which is circular and is inherited only from an individual's mother. DNA extraction is possible from either the mitochondria (mitochondrial DNA or mtDNA) and the nucleus (nuclear DNA) (18). As mitochondrial DNA is inherited only from the mother all maternal relatives have the same DNA (19). For example, if you have the same mother all your brothers and sisters will have the same mitochondrial DNA as you. DNA is comprised of four major components, called bases, each represented by the letters A, T, C and G (A -- Adenine; C -- Cytosine; T -- Thiamine; and G -- Guanine).
The structure of DNA consists of two long strands bound in a "duplex" with the entire structure coiled in a "double helix" (20). The two strands of the double helix are identical in structure but differ in base sequence. The two strands are held together by specific and mutual attraction between the bases. The sequence of bases along one of the two strands constitute the genetic code, and it is these differing combinations of A, T, C and G. which make individual DNA unique. The analysis of both mitochondrial and nuclear DNA involve an examination of the sequencing of the bases of DNA (21). At this stage the sequence or the order of the bases A, T, G and C. are examined, and it is the order that those bases appear in that makes DNA individual. In crime solving, the sequences of both the target sample and blood reference sample are examined to determine if they are consistent with each other.
Furthermore, the DNA molecule is very stable and can withstand significant environmental challenges, which enables forensic scientists to obtain new information from very old biological evidence or establish important data from badly degraded samples. These factors make DNA testing even more important in assisting to solve old crimes where evidence from the crime scene has been carefully stored. Every week on the news there are reports of how old DNA has solved a crime that occurred years ago, or how new tests regarding evidence has set free an innocent person convicted of a murder charge. Additionally, the stability of the molecule, combined with the discriminating features of each individual's DNA and the accuracy of current DNA analysis techniques, makes this human identification technology a vital component of most police investigations.
Nuclear and mitochondrial DNA analysis have proved effective in crime solving throughout the United States. The unfortunate outcome of Driskell's case can be compared to that of "X and Y." One PRIVATE "TYPE=PICT;ALT=new" December evening in 1994, a woman and her 4-month-old son (X and Y) were abducted and left to die in a wooded area in Pennsylvania. Although the woman's husband was an early suspect, detectives soon realized that he had not been involved in the crime (22). Evidence revealed the man's jealous ex-girlfriend was the police's main suspect. Due to the careful collection of trace evidence from the victim's vehicle, investigators located a hair, stained with the victim's blood, on the back of the driver's seat. Similar to Driskell's case, in the case of X and Y, hair collected from the inside of a vehicle was also the sole evidence collected. In the X and Y case, laboratory tests were performed on this hair and a sample from the suspect demonstrated that the evidentiary hair had the same mitochondrial DNA sequence as the one from the suspect and possibly could have come from her.
Later, the suspect was tried and convicted of killing both the woman and her baby. In this case, it was the mitchondrial DNA sequence that assisted in solving the crime. The FBI Laboratory began analyzing mitochondrial DNA (mtDNA) in casework in June 1996, and since that time, the DNA Analysis Unit II, using mtDNA sequencing techniques, has processed approximately 500 cases (23). Given the many different circumstances that can surround a case, sometimes advantages exist in analyzing mtDNA over nuclear DNA for forensic purposes. First, the location and structure of mtDNA protect it from degradation when exposed to the environment (24). Mitochondrial DNA is buried deep within the cell and has a circular structure, which protects it from deterioration. Also, DNA is bound and protected by a substance, called hydroxyapatite, found in teeth and bones (25). Second, the high copy number of mtDNA gives the forensic scientist a better chance of locating and amplifying a piece of undergraded DNA in a sample (26). Finally, the maternal inheritance of mtDNA can prove advantageous in cases involving missing persons, even though this fact also makes it less discriminating than nuclear DNA because any person who is a member of the same maternal lineage will have the same mtDNA sequence (27).