Biology has occupied a place of honor in the forensic laboratories, and such an easy task as a personal identification is now impossible without the usage of methods of this science. This research is focused on the most promising direction of forensics – the evidence of identification on DNA analysis results. This method is a revolutionary one, preceded by fingerprinting, but much more accurate and correct. Unless it needs a small amount of any tissue with a cell, the DNA analysis is a complicated process because even a small laboratory error may put an unguilty person into prison as it was many years ago before the discovery of the DNA. There are even the data systems of the DNA results. So, nowadays DNA identification is the most suitable, easy and reliable way in forensics.
DNA as a Magic Tool of Forensics
The introduction of biological methods of analysis in the forensic process has a long history. Serological typing of molecules in biological fluids such as blood group markers AB0 was added to the arsenal of forensic which has already contained the dactyloscopy since 1892. But the usage of DNA identification has become an evolutionary leap in the field. Considering the well-known fact of the genetic uniqueness of every person (except the identical twins), there is a widespread view of 100-percent accuracy of personal identification by DNA analysis. One would think that everything is simple: the only thing to do is to compare the DNA of a suspect with the DNA obtained from biological samples found at the crime scene. The next thing to do is to determine whether these samples fit together and in case of a positive result bring in the verdict of guilty (or free from a charge a person if there is a poor match of the samples).
However, this apparent simplicity is deceptive. There are some interesting facts obtained by comparing the not so long ago deciphered human genome with the genomes of our younger brothers, for example, only about 0.5-1% of "letters" of the genome make us different from chimpanzees. Man is different from another (unrelated) person only in one nucleotide from 300 - 400! That is we are all genetically identical at 99.99%. The first man to guess how to identify a person using the methods of molecular genetics, was an English professor Alec Jeffreys, who published in the “Nature” magazine the article “Individual-Specific ‘fingerprints’ of human DNA” in July, 1985.
The term “fingerprint” was applied by him figuratively and it had nothing in common with the traditional fingerprinting. A method described by Jeffreys is based on the ability of bacterial enzymes called restriction enzymes or restriction endonucleases or just restriction enzymes to recognize well-defined DNA sequences and cut it in areas of pattern recognition. This fact was known long ago, but the English scientist was first to discover that the length of the resulting fragments is different for different people, hence the conventional name of the method is a restriction fragment length polymorphism (RFLP). The introduction of the Jeffreys discovery which made a revolution in the forensic science has occurred in the judicial practice against the tragic events.
On November 21, 1983 a 15-year-old Linda Mann from a small English town was found dead near her house. The crime was not disclosed, although the killer had left traces of his semen on the victim's body. And three years later, on August 1, 1986 in a neighboring village there was a recurrence of a nightmare – a 15-year-old Don Ashworth was raped and strangled.
Serological identification of the semen found on the body of the second girl proved the presence of factor of phosphoglucomutase and discovered that the blood of a killer belonged to the second group. These data was consistent with the characteristics identified in the case of the first dead girl, but following them, it was possible to arraign on a criminal charge about 10% of the male population of Britain. However, some evidence testified contrarily the young (17-years-old) kitchen peddler (Richard Buckland), and he was arrested on suspicion of commitment a double murder. The suspect soon admitted his guilt. However, there was false evidence.
Fortunately, one of the officers recalled about the article in the “Nature” magazine, in which Sir Alec Jeffreys described his method for the first time, and the police asked the scientist to make a comparative analysis of the existing genetic material. The study (made by officers of FSS Peter Gill and Dave Werrett) confirmed the identity of the samples found at the both scenes of the crimes, but the suspect Richard Buckland had nothing in common with it! On November 21, 1986 Richard Buckland was the first man freed from the dock due to the genetic evidence. The real killer, Colin Pitchfork, was arrested a year later.
That was the way the personal identification on the basis of DNA analysis was introduced into criminology. It carried out two main tasks: an analysis of the consistency of biological samples found at the crime scenes with samples obtained from a suspect, and the establishment of filiation with the help of DNA. The undoubted advantage of this method is that even a negligible amount of sample is sufficient for analysis. In addition, any samples containing at least a few cells: blood, semen, saliva, hair, bone tissue may be used as the material for DNA extraction.
There are several systems with the installed standard set of loci (fragments of DNA) with the help of which the DNA identification is carried out. CODIS is an American system adopted, which includes 14 STR-loci. They are situated on the different chromosomes and their independent distribution makes the statistical analysis more reliable. The set of ENFSI is the most common system in the European countries, Russian criminological laboratories used to work with Promega system.
In regard to the laboratory errors, the possibility of which can never be excluded in the analysis, they are the cause of the growing skepticism of the public for DNA identification. Errors can occur at each stage of the expertise – from the collection of samples before making final conclusions. It’s very easy to transfer DNA from one place to another, to mix the samples, that is to falsify the results of the criminological investigation. Thus, the football player O.J. Simpson, accused of murdering of his ex-wife and her boyfriend, was pardoned and released. Despite the fact that the results of DNA analysis pointed out his guilt, the competent defense had identified the mistakes made during the investigation and examination and did not allow the court to bring in the verdict of guilt.
Thus, there are several reasons for the DNA molecule to be so attractive to the forensic identification: the uniqueness of the individual DNA, because everyone in the world is different genetically (except the above mentioned identical twins, who are essentially clones), the genetic continuity of the body (genetic information in contrast to the composition of proteins or fats does not change during the life and does not depend on the type of cells from which DNA is extracted.
The results of the molecular genetic methods in the forensic science are clear: thousands of people all over the world who spent long years in prison because of the false accusation are uncaged. And DNA identification should be invented at least for the sake of these people who regained freedom after the wrong imprisonment.
Jeffreys, A.J., Wilson, V. (1985). Individual-specific 'fingerprints' of human DNA. Nature 316, 76-79.
Butler, J. (2009). Fundamentals of Forensic DNA Typing. Maryland, USA: National Institute of Standards and Technology Gaithrsburg.
Kobilinsky, L., Liotti, T.F., Oeser-Sweat, J. (2005). DNA: Forensic and Legal Applications. Hoboken, N.J.: Wiley-Interscience.
Watson J.D. (2003). DNA: The Secret of Life. New York: Random House.
Sean Henahan. (1995). An Interview With DNA Forensics Authority Dr. Bruce Weir. Access Excellence. Retrieved from http://www.accessexcellence.org/WN/NM/interview_dr_bruce_weir.php