The three Black September terrorists that were released-after serving nominal prison sentences-after the Munich massacre.
Hezbollah has perfected this to a science.
They take someone hostage, e.g. Elchanan Tannenbaum, and then exchange them for an incarcerated terrorist from its ranks.
I guess we could hope that the Germans surreptitiously implanted a GPS tracking device in Hammadi so we can track his movements and, if necessary, terminate him with extreme prejudice. But the likelihood of that has got to be miniscule...
This seems to have been Germany's foreign policy for at least the last 40 years.
Someday the chickens are going to come home to roost and it won't be pretty.