On the eighth anniversary of his arrest over the murder of girlfriend Jodi Jones, 14, it has been reported that officials are moving closer to taking up his appeal.
Mitchell, 23, lodged his plea four years ago, claiming his rights were breached on five grounds.
Last week, the court in Strasbourg, France, asked for more paperwork to support his case before deciding whether to progress.
Mitchell’s mum, Corinne, 53, of Dalkeith, said: “The court has been considering his case for a long time and it’s encouraging they are taking it on. It’s been eight years of agony since he was taken away from us.”
Mitchell claims he was subjected to “degrading treatment” as police questioned him, had no access to a solicitor and was “bullied, hectored and intimidated” by officers.
Campaigner Sandra Lean said it could lead to another Scots appeal.