Thanks all for the responses so far.

My question was a serious one - I am intrigued; I was not suggesting for one minute that the US does not take things seriously, nor making any comment on European vs. US law and politics and the like!

I think that the ICC/Hague stuff may be what I am thinking of - thanks finboy.

Edit:

It is indeed the Rome Statute of the International Criminal Court.
The US does not intend to become a party to the treaty, whereas the UK did become a participant.

Well done, finboy.