Mr Rennie ordered the investigation into the leak and in the course of her inquiry, Ms Rebstock interviewed A.
Ms Rebstock's draft findings concluded that "there is a proper basis for strong suspicion" that A may have leaked the paper directly or indirectly.
Applicant A's lawyers, Jason McHerron, argued that the terms of reference of the inquiry did not allow Ms Rebstock to make conclusions of suspicion but said she could report on proven facts.
The Court of Appeal has disagreed and said it was within her powers to make deductions on strong suspicions.
It found that while the evidence pointing to A was circumstantial it was still a proper foundation on which to draw a conclusion.
Mr Rennie welcomed the decision, saying it meant Ms Rebstock could now finalise her report.