Bowe Bergdahl

Personally, I would rather these 5 responsible for 1000's of innocent lives face trial in the US or {cough cough} UN. To release these tyrants back on Afghanistan will prove to be a costly mistake.

A trial in the US was pretty much out of the question.
The methods used during detention coupled with US efforts to ensure US people don't end up in the Hague too rule out the UN route.
That leaves three possible routes, or 4 if you include summary execution of prisoners without trial.
1. keep them in prison without trial for the rest of their lives.
2. pay another country a large amount of money to accept them for release(the usual method)
3. swap them for a US POW.

#3 seems the best deal on price.
The costly mistake was the manner of their imprisonment and the shortsighted attempts at ignoring all the relevant laws.