I would have defined circumstantial evidence the same way as Holly did, so what is the correct definition?
Nobody "promotes murderers", as far as I'm aware, at least, not knowingly, but some of us question convictions. It's a good thing people do, otherwise MOJ's would never come to light.
Basically, under Scots Law it takes corroborated evidence to secure a conviction. Circumstantial evidence in scots law is nothing new nor is it 'inferior' in any way. It is valid evidence which most certainly does not amount to "pointing the finger".
I think it possible that had Mitchell not gone for the defence of alibi it might have left the door open for members of the the jury to presume reasonable doubt. But that door was slammed shut in theirs and Mitchell's face when his brother did not substantiate the narrative.
The Scottish Law of Evidence is a complex issue and I have seen one or two explanations provided in context by John on the forum which are worth checking out. Bearing in mind he has first hand training and experience of this.
I also recommend you type - circumstantial evidence in scots law - or words to that effect into your search engine which should provide you with accurate information.