Semen stain: How can detection of biological material help solve rape cases.
There is research suggesting that evidence containing semen on their surface can yield information even after repeated washing, something that is very important in cases such as rape. By applying the appropriate techniques and methods, the stain can even become visible, the nature of the biological material confirmed, i.e. a positive semen trace; the genetic material can even be isolated giving a reliable genetic profile. There are many variables based on which this research has been carried out, such as washing conditions of the piece of evidence (detergents, washing machine, addition of bleach). how the sample is collected from the evidence, as well as the number of washes.
It is certain, however, that the genetic profile of the donor(s)’ semen can be retrieved, even if evidence has been washed up to 6 times it is completely reliable to solve many cases!
There are, of course, findings in such studies that can create confusion. In cases where the piece of evidence has been washed in a washing machine, the phenomenon of secondary carry-over has been observed, that is genetic material (sperm cells) is transferred and detected in evidence/objects which are absolutely clean but so happen to be found in the washing machine together with the piece of evidence containing the semen. Even though, as already discussed, sperm can remain and be detected on the evidence even after several washes, some can also be carried over!
In such cases, the expert handling the case, based on relevant knowledge about the quality and quantity of the DNA, must be able to tell whether the material has been carried over or not or whether was originally deposited on the evidence.
|Articles by the DNAlogy Court Experts|
