The interpretation of traces found on adhesive tapes

In violent crimes, adhesive tapes such as duct tape are often used by perpetrators e.g. to tie up a victim. In the forensic examination of such tapes many different types of traces can be found, such as finger marks and human biological traces. These traces are first interpreted at source level. However, even when it is certain that a trace was donated by the suspect this does not necessarily mean that he donated the trace while taping the victim, as he could have e.g. used the tape roll from which the pieces came previous to the crime. Therefore, the trace can also be interpreted at activity level. For this, factors such as transfer, persistence and recovery, as well as the position of the trace as it would have been on the original roll have to be taken into consideration. In this study, we have developed a Bayesian network which can aid the forensic practitioner in his interpretation. From a sensitivity analysis, we have concluded that it would be most desirable to set up further studies to determine the most likely positions of DNA on tape rolls if there has only been innocent contact.