Hello John. I respect your opinion but I do not necessarily agree with this. Could it be that they were together earlier in the day and Jody perhaps got changed during the time she was supposed to meet him on the evening? I cannot recall under what circumstances they were together earlier on the day she was tragically killed. Were they at school together that day? If so they could have both been changed out of their school clothes. I really do not think that Luke was capable of removing every trace of his DNA whilst managing to leave other people's DNA present. That is just my opinion of course. Sorry I took so long to reply, I was locked out of my account for some reason.
They did meet in private at school earlier that day and if I recall correctly, Jodi got the bus home after school while Luke walked home alone. Nobody ever came forward to claim anything different.
One thing which those unfamiliar with the case must understand is that Luke Mitchell was seen by a passing motorist at the end of the rural track which led to the murder scene just minutes after Jodi had been brutally slashed across her throat. In fairness to the defence, Mitchell denied this was him and claimed that he never strayed from the entrance to his estate which was several hundred yards away. In order to believe Mitchell's version of events one has to accept that another lad who looked like Luke Mitchell and was dressed like Luke Mitchell just happened to be stood there, a few hundred yards from Luke Mitchell as Jodi was murdered. One also has to remember that the track was barely used and that pedestrians using the public road were few and far between.
I fear that on the balance of probabilities, the jury failed to accept this coincidence.
As for the DNA, the simple answer is that it rained on the murder scene and as Lothian & Borders Police failed to erect a canopy over the site, all sorts of evidence was lost.