DNA transfer in packaging: Investigation of mitigation strategies

Crime scene exhibits are often packaged at a crime scene and transported to a laboratory for DNA analysis. DNA-containing material may be lost from the sampling site of the exhibit to the inside of the packaging, preventing identification of a suspect, or may transfer to other parts of the exhibit complicating the interpretation of results. We sought to mitigate this DNA transfer by testing packaging that reduced direct contact with the exhibit, limited the exhibit's movement, or contained physical barriers to separate areas of the exhibit. Blood, saliva, or touch DNA were deposited onto mock exhibits that were packaged by one of four methods: unsecured, secured to bottom, secured suspended, or secured suspended with barrier separating areas. Packaged exhibits were then transported in a manner resembling casework, after which the location and amount of DNA on the exhibit and packaging were assessed. Control samples, which were not transported, were also tested. Touch and saliva deposits appeared to transfer by direct contact with the packaging and this transfer could be mitigated by suspending and/or securing the exhibits within packaging to minimize contact. Blood flaking from the exhibits meant the transfer of blood was inevitable under the conditions tested. While limiting direct contact between the exhibit and packaging minimized relocation of blood on the exhibit, the use of physical barriers prevented its transfer to other parts of the packaging. We show that while DNA transfer in packaging is not uncommon, there are strategies to mitigate this.