Are the Results of DNA Analysis Valid Evidence in A Criminal Investigation?

Since the 1980s, DNA analysis has been used for medical purposes and to resolve disputes of parentage. It was in 1988, that DNA was first admitted as evidence in court in the case of Florida vs. Tommy Lee Andrews. From 1989 onwards, FBI (Federal Bureau of Investigation) started accepting casework from Forensic Labs.
As a new technology, DNA Analysis had to be shown to satisfy certain well established standards for admissibility of novel scientific evidence. The most common standard is the Frye Rule, although a few courts use the Relevance Test, which is based on the Federal Rules of Evidence. Both standards address the question of admissibility of novel evidence, and rely on expert testimony on matters related to specialized experience and knowledge. Since DNA analysis was already in use for medical applications, the courts quickly accepted that it satisfied Frye Rule.
As of today, DNA evidence is admissible in courts of law of all nations, and has been used effectively, especially in cases of rape, to identify the guilty and to exonerate innocent suspects.
In theory, the procedure of DNA analysis is faultless. Underlying most cases where courts accepted DNA analysis as evidence, were the following assumptions:-
• DNA is present in every cell in the body
• Therefore, the sample found at the crime scene would match the sample drawn from the guilty person.
• False positive identifications are, therefore, not possible, since unless one has an identical twin, DNA is unique to a given person.
However, in practice, a number of technical and non-technical challenges are faced in DNA analysis, which are of significant concern to the process of justice.
Among the technical challenges is the fact that in medical analysis, fresh samples are available, which are drawn from a single individual. Test conditions are optimal, and in the event of a mistake, the procedure can be repeated with fresh samples. But, in case of forensic analysis, only the sample collected from the crime scene is available for processing. The sample may be degraded and may even be a mixture from two individuals, as in cases of multiple murder. A test can only be preformed once, since the sample is of limited quantity.
Furthermore, medical analysis usually poses a question such as “Which of the two RFLP alleles has a parent passed on to a child?” Since there are only two possible answers, there exists a natural consistency check to guard against error. On the other hand, forensic scientists are given two samples of which they know nothing in advance, and asked a question like “Are the two samples identical or not?” In order to answer this question, the analyst must compare the band patterns produced by the two samples. He is required to make fine judgment about whether small differences in band patterns are of significance.
Even if, after examining several sites of genetic variation, and finding an absolute match between the suspect’s DNA and the DNA from the sample found at the crime scene, one cannot declare that the sample came from the suspect. The scientists need to calculate the mathematical probability that the match of band patterns occurred by chance. For this purpose, they need to know the distribution of band patterns in the general population, which can be obtained from various databases.
Another technical challenge being faced is that of DNA fraud, wherein criminals plant fake DNA to mislead investigators. One such example is that of Canadian physician John Schneeberger, who planted fake DNA in his own body to avoid being suspected in a rape case. An Israel based company, Nucleix, has demonstrated that with access to DNA profiles on databases, it is possible to synthesize DNA without obtaining any tissue from a person. Nucleix has also developed a test for distinguishing fake DNA from real DNA with the objective of selling this test to forensic labs. But the need for this test would slow down busy labs even further. Forensic casework backlogs already pose a serious problem, with over a half million cases in backlog at the present.
Among the non-technical challenges are the public misconceptions of DNA analysis, fuelled by movies and television. Judges and lawyers notice a “CSI Effect”, wherein jurors ask for DNA analysis when there is no need of it, or disregard other physical evidence in the availability of DNA analysis evidence.
Both technical and non technical challenges are being combated, with technical advances such as expansion of databases, new procedures, training to forensic lab personnel, development of formal protocols to handle samples, and by legislations to have accountability on the part of forensic labs.
Further advances may bring some good news and some bad news (in the form of unforeseen challenges), but the real bad news is reserved for criminals, who will find it increasingly hard to escape scot free.