One of the key pieces of evidence against Sollecito is the presence of his DNA on the bra fastener of Meredith Kercher, recovered some six weeks after the original crime scene investigation. Whilst there may be a need to consider in laboratory contamination, there are several explanations for the presence of the DNA that are innocent.
If we consider mechanisms of DNA transfer examples of innocent mechanisms might include the following. Primary transfer occurs when an individual’s DNA is directly transmitted to another individual or object. It does not however imply touch; DNA can be directly transmitted by coughing or sneezing for instance. Thus it is possible that Sollecito’s DNA on the fastener of Meredith Kercher’s bra fastener might have originated from Sollecito coughing or sneezing near the bra, if for instance it was hanging up to dry, or was in a pile to be washed.
Secondary transfer occurs when DNA is deposited on a surface (including an individual) then is transferred from that surface to a second site, an example might be Meredith Kercher shaking hands with, hugging or ruffling the hair of Sollecito, primary DNA transfer depositing Sollecito’s DNA onto Meredith Kercher’s hands. She then transfers Sollecito’s DNA from her hands onto the bra fastener as she puts on her bra.
Tertiary transfer of DNA is when the DNA is further transferred to a third site. This is in fact well recognised in the medical world as a route of disease transmission. For instance medical staff who have acquired EBOLA have often done so through tertiary transmission. The virus contaminates the mask or gloves of the doctor (primary transfer), during removal the virus gets on the hands of the doctor or nurse (intact skin is not a route of entry for viruses) secondary transfer, then from the hands to mucosal membranes when the hands touch the mouth, nose or eyes. (In fact this is a common route of transmission of flu, from a surface contaminated by virus from a sneeze or cough, then to a hand, then to nose or mouth.) In this case tertiary transfer could occur (as suggested by Prof. Gill) when DNA was deposited by Sollecito on the external handle of the door to MK’s bedroom. Trying to force the door open would have provided an excellent mechanism to transfer DNA onto the door knob. Secondary transfer then occurred with Sollecito’s DNA transferring to the gloves of the forensic investigator when they touched the door knob with gloved hands, the smooth surface of the metal knob would be a good surface to pick up DNA from. Tertiary transfer then occurred from the glove to the bra strap. The ‘rough’ fabric of the fastener would have provided an excellent pick up surface for DNA.
If we consider mechanisms of DNA transfer examples of innocent mechanisms might include the following. Primary transfer occurs when an individual’s DNA is directly transmitted to another individual or object. It does not however imply touch; DNA can be directly transmitted by coughing or sneezing for instance. Thus it is possible that Sollecito’s DNA on the fastener of Meredith Kercher’s bra fastener might have originated from Sollecito coughing or sneezing near the bra, if for instance it was hanging up to dry, or was in a pile to be washed.
Secondary transfer occurs when DNA is deposited on a surface (including an individual) then is transferred from that surface to a second site, an example might be Meredith Kercher shaking hands with, hugging or ruffling the hair of Sollecito, primary DNA transfer depositing Sollecito’s DNA onto Meredith Kercher’s hands. She then transfers Sollecito’s DNA from her hands onto the bra fastener as she puts on her bra.
Tertiary transfer of DNA is when the DNA is further transferred to a third site. This is in fact well recognised in the medical world as a route of disease transmission. For instance medical staff who have acquired EBOLA have often done so through tertiary transmission. The virus contaminates the mask or gloves of the doctor (primary transfer), during removal the virus gets on the hands of the doctor or nurse (intact skin is not a route of entry for viruses) secondary transfer, then from the hands to mucosal membranes when the hands touch the mouth, nose or eyes. (In fact this is a common route of transmission of flu, from a surface contaminated by virus from a sneeze or cough, then to a hand, then to nose or mouth.) In this case tertiary transfer could occur (as suggested by Prof. Gill) when DNA was deposited by Sollecito on the external handle of the door to MK’s bedroom. Trying to force the door open would have provided an excellent mechanism to transfer DNA onto the door knob. Secondary transfer then occurred with Sollecito’s DNA transferring to the gloves of the forensic investigator when they touched the door knob with gloved hands, the smooth surface of the metal knob would be a good surface to pick up DNA from. Tertiary transfer then occurred from the glove to the bra strap. The ‘rough’ fabric of the fastener would have provided an excellent pick up surface for DNA.
