I don't know much about law. But from what I understand, the issue here is that what Touma said will not hold much value or has less value because there's already a "truth" that came out of the civil case. There's no camera inside the restroom, so they need to find out what happened inside from other sources. But the court already knows the "truth" that it was the brothers who were inside first.
Because of this Touma has doubts that his deduction can help much. After all, he can't really prove who was in the restroom first. In previous cases, Touma's logic were used to find the truth when there was none. This time, there's already a "truth".
But I think the ending implied that he will still try to explain his deduction to the police. I'm assuming if they can find hard proof that it was the guy who erased the surveillance video or he was the one who moved the corpse, the alibi can be broken.
