Low Template DNA and Criminal Trials
The use of DNA in criminal trial is commonplace and most people would be aware of what DNA is and how it might be used in court. In a rape case, for example, it might be alleged that an accused person has left some of his DNA on the clothes of his victim, in the form of saliva, blood or semen. DNA can be found attached to a hair left at the scene or the victim of a violent assault may have their DNA under the finger nails of the attacker in the form of skin or blood.
In the past, the prosecution has had to obtain a reasonable amount of DNA to provide a valid result. Traditionally, where DNA levels have been very low, for example a few cells or the DNA has degraded, it would have been usual for a forensic laboratory to conclude that there was insufficient DNA material to reliably test.
As technology has improved, however, there has been a growing trend, particularly in the United States and the United Kingdom, for prosecutors to rely on Low Template DNA as part of their evidentiary matrix. From around 2017, Low Template DNA has been used in criminal trials in Australia.
Low Template DNA is also known as Low Copy Number DNA. It involves taking very low DNA samples, levels which previously would not have been discovered, and using sensitive detection equipment and other techniques, amplifying the sample to a point where DNA components can be identified.
Such low levels of DNA are also referred to a trace level DNA.
In the laboratory, the trace sample is repeatedly tested to see whether the results received from one test can be replicated or reproduced. This is also known as cycling. The goal is to amplify the trace DNA to a point where the results can be mapped on a graph known as electropherogram or EPG. When DNA components are detected, they will show up as peaks on the EPG. DNA component material is also referred to as alleles. Different alleles will show up as peaks at distinct locations on the graph. These locations or points are called loci and are referred by an abbreviations such as D10, TH01, FGA or SE33. The height of the peak will correspond to the amount of that allele in the sample.
With the exception of identical twins, like fingerprints, everybody’s DNA is unique. Analysis of DNA when the sample contains material from only one person is relatively straightforward. It becomes more complicated when the sample contains DNA from two or more people or what is known as a mixed sample. It also becomes more problematic in situations where there is only a trace sample and that sample is mixed.
There are other issues with Low Template DNA. In such cases, DNA components may be missing, due to the low size of the sample or degradation. Amplifying the sample may cause false peaks or spikes known as artifacts – in other words, show a component where one does not exist. There is also an effect called stutter peaks. These are also false peaks that occur during the amplification process, which will appear immediately before or after a real peak.
The sample may be contaminated, which can cause a false reading.
In situations where the sample is very low, it may be difficult or even impossible to say whether the sample is from one person or a number of people.
Scientists use software programs to work out the likelihood of whether the sample of DNA came from a specific person or two or more people, which is known as the likelihood ratio.
Obviously, due to the issues referred to above, in a criminal trial, expert evidence will be relied upon to explain and challenge the results obtained by the analysis of Low Template DNA.
Chelmsford Legal was the first law firm in Western Australia to defend an accused where Low Template DNA was involved in a murder trial. We have the knowledge and access to the leading experts in this area and can readily provide legal advice and representation.