Why? His name was one-letter away from another suspect:
Khalid Al-Masri 
I'm not a fan of ICC as a solution to this problem. But it's interesting that the people behind very obvious torture/kidnapping are going unpunished.
The CIA dropped him, dirty and in ragged clothes, on some country road in Albania. Where he was detained again, because he looked like a terrorist. (!)
He's obviously broken. After returning to Germany he committed violent crimes and was sentenced to prison.
No idea why the court did not send him to a psychiatric clinic.
Which may be an equally a relevant point to this topic.
Why not, seems reasonable on the face of it.
Genuine question, not American, so maybe unaware of nuances.