Buck Rogers

On an old radio drama of Buck Rogers, Buck sent a villain back to earth to be tried for his crimes on the planet. His specific words included something about the Supreme Court.
Okay. Wait. Supreme Court? Aren't they only supposed to judge what is constitutional and what isn't?
How does this apply to a crime committed on a planet billions of light years away?
Furthermore, is causing an army of robots to attack the inhabitants of an alien planet really unconstitutional?