Bericon’s team of forensic DNA experts have vast experience providing forensic DNA services. In reviewing cases involving DNA profiles, forensic expert witnesses typically review the following aspects:
- Whether the DNA forensic scientist has followed appropriate procedures in a case From what starting point did the scientist base their conclusions?
- The quantity and quality of the DNA samples detected in this case, to what extent is it consistent with transfer by another person or object that has some of the defendant’s DNA profile on it when coming into contact with the relevant exhibits?
- It is possible that a close relative of a defendant may have contributed to the reported forensic DNA testing results?
- Provide an explanation regarding why the DNA test results are reported as “complex” and how this influences the conclusions of our forensic DNA science experts.
- Explain how the uncertainty of the number of contributors affects the reliability of the reporting of the conclusions of forensic experts.
Case Study – Key Information:
– The defendant was charged with Possession of a Prohibited Firearm.
– A police officer located a firearm inside a bag belonging to the defendant.
– The defendant was arrested and interviewed by police. He denied possession of the firearm.
– Samples from the firearm were transferred to a laboratory for DNA analyses.
– A Crown-instructed forensic scientist produced several witness statements detailing the results of the DNA analyses. In their witness statements, they reported that DNA that could have originated from the defendant was detected in the combined samples from the pistol grip of the firearm.
Expert Instruction:
Bericon’s expert was asked to comment on the findings of the Crown-instructed scientist’s reports regarding the results from the pistol grip and, in particular:
– The plausible ways in which DNA matching the defendant could have been deposited onto the pistol grip.
– The general reliability of mixed DNA profiles.
– The reliability of the mixed DNA profile identified as being connected with the defendant.
– The statistical probability analysis attributed to the defendant’s DNA being found on the firearm deposited onto the pistol grip.
Expert Findings:
It is not possible to determine from DNA results when, how, under what circumstances, or in what sequence the DNA was deposited. If the defendant had handled the pistol grip, this could explain the presence of DNA matching them in the detected mixture. Alternatively, if part of the sampled area of the pistol grip had come into contact with a surface containing a sufficient amount of the defendant’s DNA, this could also account for the findings. Additionally, the results might be explained if the defendant’s body fluid, such as from a sneeze, had been projected onto the firearm.
Generally, mixtures of DNA can be more difficult to interpret given that there can be uncertainty regarding from whom the various components in a DNA mixture may have originated. However, provided an appropriately cautious approach is taken, results from DNA mixtures may be reliably accepted as evidence. In this case Bericon’s expert was satisfied that the approach of the crown-instructed scientist was appropriately cautious.
In Bericon’s expert opinion, the DNA results from the pistol grip can be considered to be reliable.
Bericon’s expert examined the DNA mixture results and compared them with the defendant’s DNA profile. In their opinion, the reported likelihood ratio of at least one billion is a reliable and fair estimate of the evidential strength of the results regarding the defendant.
Secondary Transfer:
The Crown-instructed scientist considered the possibility that DNA matching that of the defendant could have been deposited onto the pistol grip by secondary transfer. They stated that if a handshake had occurred, they might expect to have observed more DNA from another individual than from the defendant.
Bericon’s expert agreed with them that this would be a general expectation; however, it is possible for an individual to transfer more of a someone else’s DNA when touching a surface. They agreed with the Crown-instructed scientist that DNA matching that of the defendant was the more prominent contribution of DNA in the mixture detected in the combined sample from the pistol grip, but in Bericon’s expert opinion this does not mean that the defendant must have handled the pistol grip.
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