Wasn't there a devil component in the Wembley Park stabbings? I'm also trying to recollect a young man who killed a female on the South Coast, but I can't recall at the moment.
I don't know but if the perp was unknown to the victims that would be quite damning evidence.
In Luke's case the fact he was not only known to the victim but also in an intimate relationship with her makes it impossible to say whether DNA was deposited as a result of innocent transfer ie when they were involved in a consensual relationship and what might have been deposited as a result of any foul play.
We know Jodi had been grounded during the lead up to the murder but I am assuming the pair had the opportunity to be together to and from school and at lunchtime.