RFLP was the first DNA detection method used in criminology, but it requires relatively large amounts of undegraded DNA for the successful analysis to be performed, and these demands are hard to satisfy in the most cases of the crime scenes. This method is less sensitive to contamintions than PCR but its low sensitivity and high dependance of target DNA conditions resultes in gradual replacement of this method by PCR-based techniques. In the DNA analyses aimed at the identification of the personality two main tasks may be distinguished.
The first type is the comparison of accordance of the DNA from the biologic samples collected at the crime scene with the certain genotype of the suspected person. The second type is investigation of the kinship according to the DNA characteristics. The second type analyses are common in the practice of affiliation cases, while the first is closely concerned with criminal justice and, especially, with murders or rape cases. DNA analysis may have only one of two results possible. Genetic matherial of the person under suspicion may match or mismatch the test sample.
In the case of mismatch there is strongest alibi ever possible, but match doesn't mean instant “guilty”. This result has to be confirmed by additional tests, because none of the analyses may explore diversity of human genome completely, and for the initial detection onty several polymorphic areas are used. In the USA there is CODIS system that comprises of 14 polymorphic loci, in the Europe ENSFI system (9 polymorphic loci included) is more popular. That's why coincidences are possible in rare cases (about 1 per 40 то 50 thousands of people) creating the need for the second step of analysis.
This step is less concerned with DNA analysis and is related closer to statistics than to laboratory work. The point is to estimate the frequency of certain genetic features within the population of the region. This information, if analysed properly, enables the expert to exclude coincidal matches and, thus, to avoid the unfair convictions. Genomic fingerprinting is used as a tool for investigation for the relatively short period of time. For the first time DNA fingerprinting was used in the UK in 1987, when after long series of DNA analyses man was arrested and jailed for life for the murders and rapes he had committed:
... the real Colin Pitchfork was arrested and DNA samples were taken. Sure enough, when the results came back, Pitchfork's DNA profile matched that of the semen taken from the murdered girls. In 1988 Colin Pitchfork was jailed for life for taking lives of the two young girls.  This was the first case, but not the last. DNA fingerprinting showed its applicability as a tool for investigation of the cases difficult or even impossible to be solved by the regular means.
So the methodic was added to the arsenal of british, and, in a few years, european and american police. Another advantage of DNA testing copared to casual fingerprinting is that DNA samples may be taken secretly: But mass fingerprint gathering is all but unheard of in criminal cases, said James Alan Fox, a professor of criminal justice at Northeastern University, precisely because of the probability that a print obtained from a crime scene will turn out to be someone's other than the criminal's.
(Halbfinger, 2003) And: We'd follow people as they went through Burger King, and pick up a straw they used, for saliva," [professor Fox] said. "We'd go through their trash on the sidewalk. Not everybody we got DNA on even knew it. (Halbfinger, 2003) Though many people do think that secretive sampling of DNA is the violation of their rights, this method repeatedly helps the police to discover and arrest criminals that are engaged inserial crimes:
Tim Spencer (1984-1987) aka "the Southside Slayer" was a 35-year old resident of Richmond, Virginia who viciously raped and strangled 7 people, 6 women and 1 man, the man left hanging from an overpass. Each of the crimes were somewhat different, leading Richmond police to suspect copycat killers, and in 1985, they convicted the wrong man for one of the murders. They learned it was the wrong man via DNA evidence. This was the first case in Virginia legal history to use DNA fingerprinting and it both convicted Spencer and exonerated the person wrongfully convicted.
Spencer received the death penalty.  Analyzing everything said above, we may come to conclusion that DNA testing is the powerful and extreme sensitive tool for the investigation of the difficult crimes when there is virtually impossible to uncower the truth using conventional methods of investigation. This tool helped to find and neutralize hundreds of dangerous persons and, with constant improvements of the existing methodics, will help the justice more and more.
- N. A. (2006) Innocent or Guilty? Retrieved November 23, 2006 from http://www.abpischools.org.uk/resources/poster-series/biotech/innguilt.asp