The first swabs on Sheila's hands were rejected, because they had arrived with guns, therefore there it would have been pointless for the lab to have done forensic work on them.
It's important then that the swabs were done again....BUT the pathologist had already washed Sheila down....leaving no traces of blood or powder.
However, this was never discussed at the trial, therefore the jury were not aware that the 1st swabs had been rejected and the 2nd set had been done after washing....
