The FBI`s current DNA database, known as the Combined DNA Index System (CODIS), contains case samples (crime scene DNA samples or «rape kits») and individuals (taken from convicted offenders or inmates) that are automatically compared by the system`s software as new samples are entered. As of February 2007, CODIS had produced more than 45,400 «positive results» that contributed to more than 46,300 investigations (Federal Bureau of Investigation, n.d.). However, unlike the depiction of DNA analysis in popular TV shows, DNA samples are not analyzed within the hour. On the contrary, the United States currently has a huge backlog of samples waiting to be typed and entered into the database. Some of these samples come from cases that have exceeded their statute of limitations, so even if these samples could help solve a crime, the crime can no longer be tried. It took years for forensic pathologists to develop the very precise testing procedures that allow examples like those mentioned above. Today`s processes are based on the STRs mentioned above, short tandem repetitions. A single STR used in today`s forensics is about three to five DNA bases. In the past, much longer repeated base segments were needed, ranging from hundreds to even tens of thousands. Also in the past, when DNA was isolated and separated into fragments, it was labeled with radioactive phosphorus and then examined with an X-ray sensitive film. The whole process took between six and eight weeks. In addition, DNA analysis has come a long way due to the development of a technique known as polymerase chain reaction, or PCR. This process involves heating and cooling DNA samples in cycles, which ultimately «amplifies» the DNA and makes the fragments easier to detect.
With this development (which was eventually honored with a Nobel Prize, a milestone in the history of DNA profiling), forensic scientists are able to work with smaller amounts of biological evidence. The FBI measures the success of the CODIS program by counting the crimes it helps solve. The «cold snap» (20) is defined as a game that provides the police with an investigative clue that would not have been developed otherwise. The following two cases illustrate typical CODIS results. DNA is typically used to solve crimes in two ways. In cases where a suspect is identified, a DNA sample from that person can be compared with evidence from the crime scene. The results of this comparison can help determine whether the suspect committed the crime. In cases where a suspect has not yet been identified, biological evidence from the crime scene can be analyzed and compared to the perpetrators` profiles in DNA databases to identify the perpetrator. Crime scene evidence can also be linked to other crime scenes through the use of DNA databases. DNA analysis has been instrumental in securing convictions for hundreds of violent crimes, ranging from homicide to assault.
It has also helped to eliminate suspects and led to the exoneration and release of previously convicted persons. DNA can target investigations and has the potential to shorten processes and lead to admissions of guilt. It could also deter some offenders from committing serious crimes. The increased use of forensic DNA evidence will result in long-term savings for the criminal justice system. The national and local backlog problem has two components: (1) «case sample residues,» which consist of DNA samples taken from crime scenes, victims, and suspects in criminal cases, and (2) «convicted offender residues,» which consist of DNA samples taken from convicted offenders in custody or under supervision. The nature of DNA residues is complex and changing, and it is difficult to measure the exact number of DNA samples not analyzed. The profiles stored in CODIS include a sample identifier, the identifier of the sponsoring laboratory, the initials (or names) of the DNA personnel associated with the analysis, and the actual characteristics of the DNA. CODIS does not keep a criminal record, case information, social security number, or date of birth.
Matches between profiles in the forensic file can link crime scenes. perhaps the identification of serial offenders. Based on correspondence, police can coordinate separate investigations and share independently developed leads. Matches between the files of forensic offenders and convicted offenders ultimately provide investigators with the identity of the suspect(s). CODIS also supports a population file. The population file is a database of anonymous DNA profiles used to determine the statistical significance of a match. In recent years, the federal government has strongly supported states in their efforts to clean up convicts` residues and DNA samples. Since the inception of the Department of Justice (DOJ) DNA Residue Reduction Program for Sentenced Offenders in 2000, more than 493,600 offender samples from 24 states have been analyzed. Since the inception of the Genetic Backlog Program for Suspected Cases in 2001, federal funding has been allocated to support the analysis of approximately 24,800 cases. States analyzed evidence in another 18,000 «suspect-free» cases as a result of a quid pro quo requirement to fund DNA residue reduction for convicted offenders.
The forensic community has a critical need for forensic pathologists trained in public crime laboratories. The initiative will support the development of comprehensive training programs for a new generation of forensic scientists, allowing new forensic scientists to receive in-depth training to prepare them for real-life case analysis in a forensic laboratory. The initiative provides $3 million in fiscal year 2004 to support this training. Restriction fragment length polymorphisms (RFLPs) are a technique in which genomic DNA is processed with one or more restriction enzymes that cut DNA when a certain specific sequence of bases occurs (each restriction enzyme cuts at a single restriction site); This creates a series of DNA fragments of different lengths. In some individuals, random changes in DNA result in the loss of one or more sites or lead to variations between individuals in these fragment lengths. When DNA is placed on a gel and an electric field is applied, fragments of different sizes move through the gel at different distances. The DNA can then be visualized by various methods, resulting in a gang pattern sometimes described as similar to a supermarket barcode (5). It is relatively easy to determine that two samples are different when one has a band that is missing from the other, but it is much more difficult to determine based on identical band profiles that two samples must be from the same individual. By storing DNA data in computer databases, DNA analysis can be used to solve crimes without suspects. Forensics experts can compare DNA profiles of biological evidence samples with a database to help police find suspects.
A database would also solve unsolved past crimes where DNA evidence has been found but is not linked to the perpetrator, if DNA samples taken from a suspect in a subsequent crime match evidence found at the crime scene. A national DNA database would also assist police in identifying serial offenders inside and outside the country. This second NRC report (1996) confirmed the DNA typing and statistical interpretation methods used in the United States at the time. The report stated categorically that DNA technology and gene frequency estimation methods and related statistics should not be questioned if properly collected. The 1996 NRC report addressed the issue of uniqueness of DNA typing, noting that uniqueness (with the exception of identical twins) can only be determined if all members of the population are typed. The report further recommended that, however, when a large number of loci are typed, the DNA profile obtained from the evidence may be so rare that it is very likely that a suspect with a matching profile is the source of that evidence. Those who oppose DNA banks for law enforcement purposes note that those arrested are often found innocent. Storing an innocent person`s DNA can be considered an invasion of privacy and a violation of civil liberties. It is interesting to note that in the United States, in all other circumstances, the provision of a DNA sample would require informed consent and other safeguards for the donor.
On the other hand, once an inmate`s DNA profile has been entered into a database, it can be retrieved by police, forensic pathologists or researchers without the donor`s consent. Another problem with the DNA system is the intensification of ethnic bias already present in the criminal justice system. If people from an ethnic group are arrested more frequently, tried and convicted of crimes, they will be over-represented in the database, which could lead to even more arrests within that ethnic group. To use STR information as a means of human identification, the FBI determined how often each allele of each of the 13 basic STRs occurs naturally in people of different ethnic backgrounds. To that end, the FBI analyzed DNA samples from hundreds of Caucasian, African-American, Hispanic, and Asian unrelated individuals. Assuming that the 13 STRs follow the principle of independent sorting (and they should, because they are widely dispersed throughout the genome) and that the population mates randomly, a statistical calculation based on the STR allele frequencies determined by the FBI shows that the probability of two unrelated Caucasians having identical STR profiles or so-called «DNA fingerprints» is about 1 in 575 trillion (Reilly, 2001). It takes more than DNA to convict a person for a crime. Forensic psychology, for example, is always an integral part of the process.