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The bra fastener: a case study in how not to handle DNA evidence


Police videotape taken on November 3, 2007, showed a bra fastener lying on the floor of Meredith's room, next to where her body was found.  It had been cut away from the bra she was wearing when she was attacked.  At that time, investigators apparently did not think it was important enough to bag as evidence.

On December 18, when police returned to the crime scene, they found the bra fastener at a different location in the room and collected it as evidence.  It was then subjected to DNA testing, which revealed microscopic traces of DNA belonging to Raffaele Sollecito as well as at least three other unidentified people.

This DNA test result is central to the prosecution's case, because no other evidence links either Raffaele or Amanda to the room where the murder took place.  

But how reliable is this evidence?  Raffaele had been on the premises several times and would have left his DNA on door handles and other surfaces.  It could have been transferred to the fastener in any number of ways — especially as this article remained on the floor for more than six weeks while investigators went in and out of the room.

Bra fastener -- November 3 position

The bra fastener was caught on videotape November 3, 2007.  
It remained on the floor until December 18.  During that time it was kicked, swept or otherwise moved to a different location in the room.
Bra fastener -- December 18 position

Video shows that police made a mess of Meredith's room.  More than six weeks after the murder, investigators found the fastener when they sorted through this pile of clutter.  After noticing it, two investigators handled it extensively before dropping it into a plastic evidence bag.  

Current DNA testing procedures are extremely sensitive.  The smallest particle of biological material can contaminate a piece of evidence.  One set of guidelines for avoiding such contamination is put out by the US Department of Justice, as follows:

  • Wear gloves. Change them often.
  • Use disposable instruments or clean them thoroughly before and after handling each sample.
  • Avoid touching the area where you believe DNA may exist.
  • Avoid talking, sneezing, and coughing over evidence.
  • Avoid touching your face, nose, and mouth when collecting and packaging evidence.
  • Air-dry evidence thoroughly before packaging.
  • Put evidence into new paper bags or envelopes, not into plastic bags. Do not use staples.
http://www.ncjrs.gov/txtfiles1/nij/bc000614.txt

The investigators who picked up the bra fastener did not change gloves or use a clean instrument.  Nor did they avoid touching any part of it.  

The prosecutor claims the bra fastener is proof of Raffaele's involvement in the murder.  But the defense has produced experts who have testified convincingly that this evidence proves nothing, because it has been hopelessly compromised by mishandling.