The potential for investigator-mediated contamination to occur during routine search activities.

The sensitivity and discrimination power of modern DNA profiling systems means that very small amounts of DNA from an individual can be detected on an item leading to large inclusionary statistics for that person. The sensitivity of these systems has significant benefits in the investigation of crime but also can be highly sensitive to contamination of exhibits or crime scenes. It becomes critical to distinguish between deposition during commission of a crime or deposition via some other method unrelated to the crime. This study investigates methodologies used in crime scene examination and the potential for them to cause non-crime-related transfer of DNA. Factors assessed include the source of DNA, the handling time, the amount of movement during contact, and the substrate type. The amount of movement and the number of transfer steps are the most critical in determining whether, and how much, DNA is transferred. This study provides information for crime scene examiners and also scientists assessing transfer scenarios.

Transfer and persistence of DNA on items routinely encountered in forensic casework following habitual and short-duration one-time use.

Empirical data obtained from controlled experiments is necessary to ensure that sound expert opinion evidence is provided regarding transfer and persistence of DNA in criminal proceedings. Knowledge in this area is also required at the outset of criminal investigations, to ensure that the proposed examinations can assist with answering questions that are relevant to forensic investigations. This study aimed to provide such data by examining the relative and absolute quantities of DNA deposited on items that are routinely submitted to the forensic laboratory by a habitual user, defined as someone who used it for ~1 week, and a subsequent one-time user. We found that the quantity of DNA deposited on routine household items spanned a broad range. The habitual user's DNA was detected on most items as the major donor, regardless of whether it was subsequently handled by another person for a short period of time. The one-time, short duration, user's DNA was detected on approximately two thirds of the items, albeit typically at quantities lower than the habitual user. Most of the household items we examined also had detectable DNA deposits from at least one other, unknown individual, typically in low quantities. Attempts to clean non-porous items with readily available household cleaners were partially effective but failed to completely eliminate detectable DNA from a habitual user in most cases.

The importance of considering common sources of unknown DNA when evaluating findings given activity level propositions.

Evaluating forensic biological evidence considering activity level propositions is becoming more prominent around the world. In such evaluations it is common to combine results from multiple items associated with the alleged activities. The results from these items may not be conditionally independent, depending on the mechanism of cell/DNA transfer being considered and it is important that the evaluation takes these dependencies into account. Part of this consideration is to incorporate our understanding of prevalent DNA and of background DNA on objects and people, and how activities can lead to common sources of unknown DNA being deposited on items. We demonstrate a framework for evaluation of DNA evidence in such a scenario using Object-Oriented Bayesian Networks and apply it to a motivating case from South Australia.

Validation of a neural network approach for STR typing to replace human reading.

A typical forensic laboratory process for interpreting STR capillary electrophoresis profile data is for two people to independently 'read' the profiles, compare results, and resolve any differences. Recently, work has been conducted to develop a machine learning tool called an artificial neural network (ANN) to carry out the same function as a human profile reader, by classifying areas of fluorescence in the capillary electrophoresis profile raw signal data. The ANN approach has been embedded in commercial software FaSTR™ DNA to read GlobalFiler™ DNA profiles. The ANN feature of FaSTR™ DNA was investigated during validation at Forensic Science South Australia (FSSA) to determine whether one of the human profile readers could be replaced by an ANN reader. FaSTR™ DNA accuracy in detecting allele peaks in reference profiles was 99.7% and was deemed high enough that a one-reader workflow could be implemented into the reference reading workflow at FSSA.