Forensic DNA Expert Witness Case Study 7

Independent forensic expert evidence in a DNA case

Bericon Forensics was instructed to provide independent forensic expert witness evidence in a criminal case involving disputed DNA findings.

The defendant had been involved in a fight with another man. The complainant alleged that the defendant had grabbed his head with both hands and bitten off part of his ear.

A scenes-of-crime officer attended shortly after the incident, photographed the scene and recovered blood and the detached earlobe. The earlobe was submitted for forensic DNA examination.

The forensic expert’s instructions

A forensic DNA expert witness was asked to examine the earlobe and assess whether the DNA evidence supported the allegation that the defendant had bitten it off.

The forensic expert considered:

• the mixed DNA profile recovered from the earlobe;
• whether the defendant could be included as a possible contributor;
• the significance of the low-level minor DNA component;
• whether the result was suitable for statistical evaluation;
• when and how the DNA may have been deposited; and
• whether secondary or indirect DNA transfer could provide an alternative explanation.

Independent forensic DNA examination

The forensic expert agreed that the defendant was a possible contributor to the low-level component of the mixed DNA profile obtained from the earlobe.

However, the minor DNA component was present at such a low level that it was unsuitable for robust statistical evaluation using traditional interpretation methods.

The presence of the defendant’s DNA therefore did not, by itself, establish that he had bitten the complainant’s ear.

The forensic expert also explained that DNA evidence cannot usually determine precisely when or how biological material was deposited.

Alternative transfer mechanisms were considered. The defendant’s DNA could potentially have reached the ear through prior physical contact during the fight, even if another person had caused the biting injury and had failed to deposit detectable quantities of their own DNA.

Expert witness conclusion

The forensic DNA expert witness concluded that the findings could not establish when or how the defendant’s DNA had been deposited on the earlobe.

Although the defendant could not be excluded as a possible contributor to the mixed profile, the low-level DNA result did not provide reliable scientific evidence that he had bitten off the complainant’s ear.

The expert report identified the limitations of the DNA evidence and explained credible alternative mechanisms of transfer.

Case outcome

The prosecution offered no evidence.

This case demonstrates why DNA evidence must be interpreted within the full circumstances of an alleged incident. The detection of a person’s DNA on an item does not necessarily prove the action said to have caused its deposition.

Instruct a forensic DNA expert witness

Bericon Forensics provides access to experienced forensic DNA experts and expert witnesses for criminal cases involving:

• mixed DNA profiles;
• low-level and trace DNA evidence;
• DNA transfer and secondary transfer;
• DNA persistence and deposition;
• blood, saliva and cellular material;
• interpretation of statistical findings;
• review of prosecution DNA reports;
• assessment of alternative transfer mechanisms; and
• independent expert witness reports.

Our forensic DNA experts can assess the scientific findings, explain the limitations of DNA evidence and prepare clear reports for solicitors, counsel and the court.

Contact Bericon Forensics to discuss the instruction of a forensic DNA expert witness.