So you're implying that Ruritarian law includes explicitly laws against bombing foreign lands? How else do they try and lock him up? For the act of abusing the mail or the act of creating the bomb? I don't see how they can try him for the bombing itself -- it's not their country, not their jurisdiction.

I believe that jurisdiction matters, and where a crime is committed is jurisdiction.

I don't understand the jurisdiction grounds that Ruritaria would have on crimes committed in other countries.

If I were Poronian and a Ruritarian bombed my country and his government shielded him from Poronian justice -- I would call on my government to get his head. He gets tried in Poronian courts or he gets tried by Poronian missiles. But you don't get to commit a crime in Poronia and avoid the legal repercussions...