I don't agree 100% with your post, but i do mirror a number of the points you have made as i too feel (discussion in general aside) that there is an odd sense of determination to condemn which i too find quite uncomfortable.
I had this very conversation last night with a friend last night - i specifically said it worried me to think that a jury (which is by all accounts a random cross section of members of the public) could potentially be made up of people who seem to see things without shades of grey, or get 'nervous' or 'on edge' at the thought of a not guilty verdict. To me that isn't a jury.
There is something about this trial which still doesn't sit right with me. No matter who you look at it, there is fundamentally a lack of concrete evidence against the accused, and whilst his defence to some may seem far fetched it is a defence which has been successfully proven in other cases. It is also something that one of the experts deemed 'technically possible'.
It boils down to this. Either the 16 year old on the stand is a one-in-a-million, acutely advanced psychopath, with the potential to kill again, or there is something far more fundamental at the root of this case. My inclination is to go with the latter.
My gut feeling is, the lack of carelessness in terms of evidence at both the abduction site (the MacPhail's home) and the accused's own home does not add up with the obvious carelessness at the murder scene. Regardless of how you look at this, it simply does not fit.
Lastly, i see no motive. I think the idea that he had been planning this throughout the day is as far fetched as it gets - if he was, he certainly didn't plan particularly well given the mess that was left at the murder scene. However, i do see motive in certain other people involved.
I agree with everyone that justice for Alesha MacPhail is of the upmost importance, but if the wrong person is convicted, that in itself is doing that poor little girl the biggest injustice that could be done.