During samples that are taken from a crime

During a murder case trial, we often see both the prosecutor
and attorney presenting the evidence such as DNA evidence that they have found
on the crime scene and eyewitness testimony to the judge before he decided the
outcome of the trial. 1 This makes us wonder about the possibility that these
DNA evidence and witness testimony could be wrong and which one is more
superior compared to the other in solving crime cases. I would like to discuss
the value of DNA evidence vs witness Testimony in the next few paragraphs.

DNA evidence refers to DNA samples that are taken from a
crime scene to go through processes such as PCR test to determine the
probability of this DNA belong to specific individuals. These source of DNA
samples came from sweat, hair, blood, saliva or skin cells that are found at
the crime scene. DNA samples contain specific information such as from the
colour of the eyes to the genetic defect that an individual had. Since the DNA
of each person is unique, DNA has often been used to solve past and present criminal
cases. 2 Although DNA evidence is regarded as one of the major key players in
solving cases, it is not infallible. Human error cannot be to rule out in DNA
evidence. As human perform the test there is always a room for error, even more
so when they required meticulous and difficult techniques to analysed these DNA
samples. 3

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The contamination from secondary DNA transfer is another
limitation to DNA evidence and it is proven to be a concern in the world of
Forensic Crime investigations as there is a possibility that the ‘touch DNA’ (a
genetic or biological material found on the object due to direct contact) might
come from an unrelated individual and this will complicate the investigation.
Cynthia’s experiment proved that there are 85% chances that Person A are able
to pass person B’s DNA into an object after person A Touches Person B for short
period of time and in one-fifth of the case, only person B DNA is found as the
sole DNA contributor for this object. 4 8

On the contrary, witness testimony refers to an account of
bystander or victim describing what they observed in regards to a specific
incident that is under investigations such as the description of the
perpetrator. Before DNA evidence exists, witness testimony is one of the major
key players in solving criminal cases. However, people started to questions the
reliability of these testimonies. 5 In 1932, Bourchard has reviewed several
cases of wrongful convictions which commonly caused by false identification of
a suspect. 6 Report from Innocence Project supported this theory, 50% out of 75%
overturned convictions due to DNA evidence, is caused by conviction from eyewitness
testimony. 7 There are several factors that can reduce the accuracy of
witness testimony and one of them is biased. Biased
refers to a mindset that is in favour or against a certain group or things
compared to the others. For example, some people will have a difficulty in
identifying and remembering people of their own race compared to those of a
different and less familiar race.

Another factor that can
reduce the accuracy of witness testimony is stress. Several experiments have
proved that a person under high-stress level will have difficulties in
recalling a specific information or even make an accurate identification. Thus,
stress is able to impair the memory of a person. With different stress level
involved, witnesses from a non-violent crime will be likely to be able to
identify and remember specific information compared to witnesses from violent
crime cases. 57

In Conclusion, despite the limitations that DNA evidence had
it is still far more reliable compared to witness testimony. This is because witness
testimony heavily relies on the memory that they have seen thus it is much more
difficult for us to detect the accuracy of this testimony but the chances of
human error can be reduced by ensuring that every single DNA evidence is
validated before it is presented to the court. However, this will slow down the
forensic lab thus resulting the perpetrator could be walking on the street
freely while their DNA is still in the queue waiting to be tested.