I don't think you know a great deal about the case ~ neither do I ~ and neither does anyone who didn't sit through the evidence being presented in perhaps the longest trial of a single person ever held in Scotland.
The members of the jury did and they delivered a majority verdict which was both considered and lawful. A verdict which has since been upheld on appeal.
Mitchell's advocate was considered as the foremost in Scotland but it seems not even he could prevail against the sum and substance of the evidence presented which convicted Mitchell; foremost of which was his false alibi.
All my knowledge of the case has been gleaned from the internet, newspapers and Sandra Lean's book, so you're right, I only know a limited amount.
I would love to know what came out at trial, and I am very interested in hearing the views of people who live local to where the crime took place. Sometimes they know things that the rest of us haven't heard about!
I suspect, however, that what was presented at trial may not have been the whole story. I'm never going to actually know that, though!