According to Murphy (2005), DNA typing is one of the new forensic technologies that have widely been used in prosecution processes. He notes that other technologies that have been used alongside of the DNA test include biometric scanning and cell site tracking. Together, these technologies are increasingly being applauded for helping to detect the cases of those who were convicted unfairly as well as exposing the cases where the criminal justice had failed to convict a person because of unreliability of then available forms of evidence. However, Murphy (2005) notes that even with the majority of advocates voicing their support of this new evidence, others have warned that relying on the DNA evidence alone in an investigation and/or a trial is not appropriate. This paper will therefore examine the claim that DNA is not credible evidence.

There has therefore been a very controversial debate among the law practitioners, doctors, and other interested parties with a portion insisting that DNA evidence is credible enough while others insisted that as the process of its collection and testing is subject to human error and biasness, the evidence cannot be used on its own. Murphy (2005) on his part emphasized that even though DNA typing offer an unprecedented degree of certainty and reliability, whenever it is used, it might be subject to misuse by the criminal justice system.

Lofland (2007) noted that the numerous human errors that characterize the use of the DNA evidence may lead to numerous cases of appeals in courts. According to him, this is because there may be cases where the real perpetrators are wrongly being set free forcing the attorneys to file appeals. He therefore argues that the only remedy would therefore be the incorporation of other forms of evidence alongside the DNA evidence. This would allow the investigators to take care of the totality of all the circumstances surrounding a given criminal act.

Another argument has also been that, the mere fact that one’s DNA has been found at the scene where the crime was committed does not mean that it was this person who had committed the crime. Lofland (2007) however noted that there is a common agreement that the DNA location is of great assistance in cases where the fact about a chain of events like that surrounding murder cases is to be established. He argued that in such a case, a combined number of evidences like that from a victim and someone else found away from the scene of the murder could be suggesting that there had been a struggle between the two at the scene of death.

Malcom (2008) also notes that in cases where there is a combination of incriminating evidence, the suspect may not find it easy to escape justice since such presents the best case against him/her. A good example is a case where a suspect’s DNA has been found in a home belonging to a victim of rape along with certain tools that are suspected to have been used to aid in committing the crime like handcuffs. He notes that in cases where proofs are connected, the evidence will be much more convincing than in cases where there are no such connections, which would require additional methods of investigation to ascertain the claim.

Another strength of DNA as an evidence is legal requirements attached to its use. Lofland (2007) notes that every prosecutor basing his/her proofs on the DNA evidence must seek to be sure that their cases are solid. This is because the judge should always be convinced that the duly procedures were followed when collecting and testing the samples. He observes that even with such approvals, the attorney is required to prove that the evidence being presented genuinely implicates the suspected person and that he has no doubt about that.

Why DNA May not be Credible Evidence

Fisher (2011) notes that from the past, the attorneys who are defending the victims had been assuming that any DNA evidence presented to them is clear and can never be disputed. However, research by such bodies as Forensic Bioinformatics Services, Inc. in Ohio has found evidence proving that the DNA test is never perfect.

The first problem that has been identified concerns the durability of DNA. Michaelis et al. (2008) has argued that based on its durability, DNA presents a number of problems for statutes of limitation, which prevent the use of overlay stale criminal charges. Such statutes are put in place to guarantee high quality of the evidence used in the prosecution process because there is always a tendency for witness recollections and other evidences with time. It also ensures that defenders do not have to depend on old and in some cases unreliable sources in their bid to prove their case in defense. Michaelis et al. (2008) has also argued that the DNA evidence cannot fit within the time frames that are in use traditionally because they normally outlive other forms of evidences. This has forced certain jurisdictions to extend the limitations in their statutes to allow the application of the DNA evidence.

American Bar Association (2007) however notes that such provisions result into an additional burden for the affected defenders who will have to use old and sometimes outdated evidence against the DNA evidence, which by then will still remain to be credible. The association notes that this means that any match between the defendant’s profile and that of the DNA evidence can obviously make the defendant to lose the case. This is irrespective of the cases where the defendants had lost their witness during long proceedings as what normally counts for the Jury, is the DNA evidence. However, Fisher (2011) warns that under certain circumstances, there may be a match between the DNA profiles of an innocent person who was not even at the scene of crime, and the sample evidence. He therefore emphasized the need to review all the evidence surrounding any case before declaring a suspect as guilty.

According to Thompson et al. (2003), another weakness of DNA as an evidence is found in the current trend among the law practitioners to assume that the initial problems surrounding the DNA evidence have been resolved, and that the test is currently unquestionable. The scholars warn that such an assumption has hindered case-to-case variation as far as the nature and quality of the DNA evidence are concerned. They add that even though the technology has experienced great improvement, producing more accurate results, this has not been the case with every single case.

Michaelis et al. (2008) concurs with them when he notes that even in the cases where there has been an establishment of reliability and admissibility of the ongoing test, this does not guarantee that the results will be reliable every time the method is used. Thompson et al. (2003) went ahead and identified certain instances under which problems have been experienced in case-to-case issues leading to adverse effects on the quality of the test results. Moreover, they note that of more concern is the knowledge that the present system of criminal justice is not well equipped to distinguish between powerful DNA evidence and weak ones, which may sometimes be misleading. They argue that this has also partly happened due to inexperienced lawyers who usually fail to adequately evaluate the DNA evidence presented in the cases they are handling.

Thomson et al. (2003) have also identified the reasons why the lawyers should avoid simple acceptance of the lab reports and instead examine to learn if the conclusions made by the laboratory are fully supported by the actual results obtained through the test. They note that there have been such problems like inconsistencies between some profiles, which had been said to be matching. Other errors that normally do occur include statistical computation related errors and those problems related to control experiments, which might have raised doubts on whether the result is valid or not.

Thomson et al. (2003) argue that even if the present DNA tests are conducted using computerized equipment, the results are interpreted by man under a subjective judgment. This means that whenever the scientists face a situation allowing the call to go in any direction, analysts usually make their conclusions in line with the prosecution theories. Additionally, there is a tendency of the forensic scientist being influenced by government officials with the purpose to interpret the results according to the expected outcomes. Thomson et al. (2003) observe that there have been cases when laboratory analysts possessed full knowledge about the case and thus proceeded with his work simply to justify the expected results.

Thomson et al. (2003) have also argued that in most cases people will also ways see what they expect to see, whenever they are confronted with the need to evaluate some ambiguous data. They further note that during the interpretation stage, analysts always have to analyze certain evidences that are non-genetic, like a case where the evidence presented by the police appears to be so convincing that to them, the DNA test is being carried out for the sake of formality. In such a situation, the DNA evidence cannot be taken as credible.

Thomson et al. (2003) have argued that another reason to doubt the credibility of DNA is found in the ambiguity that always characterizes its interpretation. Firstly, sources of such ambiguity are found in the complication that comes with having to analyze the DNA evidence from more than one source. This is a case where a sample contains a DNA of more than one individual. Such mixtures are often not easy to interpret because it is hard to tell the number of people who may have been involved in committing the crime. Another problem associated with a mixture is the difficulty in telling who the primary and the secondary contributors were. Thomson et al. (2003) therefore advise that lawyers should be concerned about how the computations of the statistical estimates related to such cases are being assessed. As such computations are, in most cases, based on debatable assumptions that may cause their defendants to lose the case unfairly.

Another source of ambiguity in the DNA interpretation is degradation, which results from the aging of DNA samples. According to Michaelis (2008), this causes the sample’s chemical content to degrade, especially where such samples are not well preserved. They observe that degradation has an adverse effect as it results into skewing of the initial relationship between the present DNA quantity and the peak heights. This means that it would automatically make it difficult to detect the longer DNA sequences, which are repeated. Thomson et al. (2003) note that there were some cases where degradation has greatly reduced the peak heights to the extent that they became too low to be distinguished in a reliable process. Michaelis (2008), on the other hand, notes that in some cases, the peaks may even disappear completely.

Additionally, it has at times been impossible to find out whether the alleles of a given contributor are not yet detected at a given loci. Such cases also leave the analysts with the only option of gazing whether or not they have been detected. This means that the kind of conclusion they draw will simply be a speculative leaving room alternative interpretations, thus compromising the credibility of the DNA evidence (Thomson et al., 2003). Other cases include that of spurious peaks, which always fail to indicate the presence of DNA and the “noise”, which can also result into small random flushes though, in certain occasions, they may appear large causing confusion with the actual peaks (Thomson et al., 2003).


In conclusion, it is clear that irrespective of considerable criticism, the use of the DNA technology as an evidence has been very instrumental to the justice system. It has, for example, helped to narrow down the gap between the closed cases and those crimes, which have not been detected. Furthermore, with the evident continued increase in the proficiency of testing, cases will be resolved in a more rapid manner limiting the chances of cases piling up in the court for a longer period of time. This will without any doubt provide the police with additional time to work on other pending cases.

However, the credibility of this evidence will continue to depend on the way the limitations compromising the credibility of the DNA evidence are handled. There will especially be the need for strict measures to guide the testing and interpretation of evidences to limit the effects of such factors as ambiguity. Finally, based on the findings in this write up, DNA evidence should be used alongside of other forms of evidence to make the process more credible.

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