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  • The potential impact of multiple washings on

    2020-10-17

    The potential impact of multiple washings on DNA retention in semen stains had not previously been addressed. In the present study, multiple washes of semen-stained cotton cloth produced only a minimal loss of recovered DNA suggesting that multiple washes may not materially affect DNA recovery (Fig. 2). These results suggest that, in casework with items of clothing on which semen is believed to have been deposited prior to laundering of the clothing, it would be appropriate for items to be analysed for DNA, possibly irrespective of the number of times the clothing has been washed. However, these are preliminary data, and further work is required to establish whether multiple washings would reduce DNA recovery under other conditions, such as with varying initial semen deposits (either with respect to volume or sperm count) or on different types of material. This clearly has implications for casework where the original volume of semen or number of sperm Carprofen deposited will be unknown. In casework, there are essentially three ways to screen an item for the possible presence of semen prior to potentially preparing samples for microscopic analysis: a visual examination for appropriate-looking stains, an examination with an alternate light source, and presumptive testing, such as Acid Phosphatase (AP) testing. Under the specific conditions of this study, the semen staining was still visible even after multiple washes, suggesting that visible screening might assist scientists to identify possible semen staining on washed clothing. However, further research is required to see whether the staining would still be visible under different conditions. With respect to AP testing, previous research has consistently shown that semen-stained items of clothing laundered with detergent does not give a positive AP reaction [6], [7], [8], [9], so AP testing would not be appropriate when examining clothing washed after the deposition of semen. The use of an alternate light source to identify semen stains on washed clothing has yet to be considered and research into its use under such conditions would be useful to help inform the best way to screen such items for semen. The inclusion of unstained socks in washes with semen-stained clothing provides preliminary data of secondary transfer of DNA from the stained items of clothing to unstained items. Complete DNA profiles matching that of the semen donor were found on the majority of the socks (Table 3). This finding supports the recent presentation by Noël et al. [15] who found that interpretable male DNA profiles could be obtained from pristine panties that had been washed with a bed-sheet stained with semen. However, further work is required to investigate whether the sperm cells themselves are being transferred or whether just the DNA from the sperm cells is transferred. The additional finding of alleles that could have come from the regular user of the washing machine on two of the socks washed at 60°C suggests that DNA has also been transferred to the socks from the washing machine. This supports the concept of transfer of ‘wearer DNA’ between items of clothing in a washing machine, which had previously been proposed by Stouder et al. [16], but has yet to be demonstrated empirically. Further research is required to establish whether the nature of the semen staining (for example, whether the stain is visible or whether sperm cells are identified, and if so, the number of those cells) or the quantity of DNA obtained from the stain post-washing could be used to suggest whether the staining is as a result of primary deposition or secondary transfer within the washing machine. Depending on the case circumstances, such research, including this initial study, will assist forensic scientists in evaluating the findings of DNA from semen-stained clothing.
    Conclusion In ICST cases, it is common for offenders to ejaculate directly onto their victim’s clothing, for victims to be wearing school uniform at the time of the assault, for multiple offenders to be involved, and for victims to hide their stained clothing for lengthy periods of time before laundering them. This study demonstrates that complete DNA profiles can be obtained from laundered semen stains on school uniform-type clothing, even with an eight-month lag time between semen deposition and laundering. On cotton T-shirts, complete DNA profiles can also be obtained after Carprofen multiple washes of semen stains and from laundered stains of two semen donors. These data emphasise the need to recover and examine the clothing of victims for semen and DNA evidence, even if the clothing has been stored for several months or washed multiple times. Potential ICST victims\' clothing may be examined to locate possible semen stains using an enzyme presumptive test: this enzyme activity will be lost with washing which may be problematic for the investigation. Nevertheless, in this study, staining was visible even after washing and differentially stained areas could be targeted for DNA tests in forensic analysis. The recovery of such evidence may be crucial to ICST cases, given that the majority of these cases rely heavily on victim accounts and testimony with forensic evidence being rare [3]. These findings are also applicable to other sexual assault cases and indicate that evidence recovery should be included in investigations even if a lag time between the offence and its investigation has taken place.