Evaluation of indirect transfer mechanisms of semen under varying test conditions.

There is limited data available on the subject of indirect transfer of non-visible body fluids, particularly semen, and often forensic science practitioner experience alone must be used to guide expectations. It can be difficult to assess the likelihood of proposed transfer scenarios without knowledge of how different variables can affect a transfer. The following work carried out by the Association of Forensic Service Providers UK and Ireland Body Fluid Forum explores how the features of transferred semen change with differences in the primary and secondary surface (porous and non- porous), different contact types (passive, pressure and pressure+) and with wet and dry primary stains. It was concluded that the primary surface type and whether the stain was wet or dry when contact occurred had the most significant effect on the transfer of semen, with wet transfers and transfers from the tested non-porous surface producing significantly more, and larger, visible stains under white light, stains with stronger fluorescence as viewed using Crime-lite® ML2, stains with stronger and faster acid phosphatase reactions and greater numbers of spermatozoa viewed using high power microscopy, compared to dry transfers and transfers from the tested porous surface. Pressure with movement transfers resulted in significantly more visible stains under white light and greater numbers of spermatozoa viewed using high power microscopy compared to passive transfers, however this only occurred when transfers were from a porous primary surface. The secondary surface type was not found to have a significant effect on the numbers of spermatozoa viewed using high power microscopy.

Enzyme activity, DNA degradation and drying times of semen, saliva and vaginal material.

The stability of enzyme activity and the amount of detectable DNA within liquid samples of semen, saliva and vaginal material were tested across a number of days. The concentration of DNA within neat semen and saliva samples fell significantly after one week of refrigeration. No apparent change in acid phosphatase or amylase enzyme activity was observed in neat semen and saliva samples over 96 or 72 h respectively. Changes in the enzyme activity of most of the dilute semen and saliva samples, as well as the neat vaginal material sample, were noted after 24 h. The drying times and sizes of stains produced from various volumes of neat semen, saliva and vaginal material were tested on porous and non-porous surfaces at room temperature. Larger volumes of body fluid took longer to dry and generally resulted in larger stains. Body fluids on a non-porous surface took longer to dry than on the porous surface tested.

Assessing the background levels of body fluids on hands.

Forensic scientists are often asked to assist the court by evaluating the significance of finding body fluids on the hands of an individual; however, there is an absence of published data regarding the background levels of body fluids on hands. Whilst the scientist can use casework experience to inform the courts on the significance of the results, it would be advantageous to have data which could assist with this interpretation. This study was designed to ascertain the background levels of blood, semen, saliva, hairs/fibres and staining/debris on hands in the general population by sampling from delegates attending a scientific conference. The findings suggest that approximately one third of the population would be expected to have hairs or fibres on their hands and that females are more likely to have visible staining on their hands than males. Presumptive tests for blood and semen yielded negative results in all samples; however, almost 2 % of the samples were found to contain a very low number of sperm heads. In contrast, the majority of samples tested positive for the presence of saliva using the presumptive Phadebas® amylase test. The data supports the caution applied by forensic practitioners when evaluating the presence of saliva detected using the presumptive Phadebas® amylase test based on the lack of specificity and indicates that the RSID™-Saliva test would be more suitable to use.

Examining the transfer of male DNA onto female underwear in simulated non sexual social interaction versus digital penetration to assist in the evaluation of results in casework scenarios.

Experiments have been carried out by the UK and Ireland Association of Forensic Science Providers Body Fluid Forum (AFSP BFF) to determine the levels of male DNA, detected during Y-STR analysis, that may be expected on female underwear from non-sexual social interaction and digital penetration, versus non-sexual social interaction only. The data obtained strongly supports the existing assumptions made: whilst low levels of DNA may be inadvertently transferred to the inside surface of a female's underwear during social interaction with a male, there is a low expectation of detecting a matching Y-STR profile to that male, which is suitable for statistical evaluation, unless he is a co-habitant of that female.