From the viewpoint of the responsible German judge this release was for sure no betrayal on the US.
Hammadi was probably about more than 15 years behind bars. This is the usual timespan were killers are released in Germany. He also would have been freed if he would have killed Germans. I doubt that it has anything to do with the recent release of this woman in Iraq since Hammadi was -to my knowlege- a shiite. The hostage was a German woman that was hijacked by some sunni criminal idiots who wanted to press out money. Merkel probably paid. This is another party.
You should see the different judicial attitudes on both sides of the Atlantic. Furthermore it is nothing new that official Germany (no matter if Schroeder or Merkel is involved) doesn't feel itself engaged in the war on terror. Therefore this is simply a quite normal process. It has absolutely nothing to do with any backstabbing.
BTW - I would have disposed him quietly in the mediterranian.
The point is it appears to us that you guys just don't get it.
We could use some help you know.