Actually it's commonplace in national laws rather than absurd. Each nation has a right to set its own laws within its borders. For example, the US could make a law prohibiting US citizens and lawful residents from smoking pot when in the Netherlands even though it's legal there. If those people return to the US after smoking pot there, then they can be prosecuted for violating that law. The hard part, obviously, would be establishing the violation given the evidence is in the Netherlands. But if the Dutch wished to cooperate with the US on that, they could. Most countries don't pass or enforce laws like that, thankfully, because it's bad international relations, tough to enforce, tough or unable to get cooperation, etc, unless the subject is of the most serious and universally agreed nature. But if you're a US citizen flying to Thailand or some other place to have sex with children in the shady sex industry, that kind of thing does get prosecuted in the US with or without the help of such countries. Some countries, like the UK, allow its laws to prosecute their own citizens for murder if they commit a murder while abroad if and when they return to the UK (they usually only do this if the nation where it happens is unable or unwilling to prosecute for the murder(s)). Sometimes countries will pass laws and take actions in other countries even if the other nation is opposed and unhelpful. For example, the US will prosecute US citizens who spend any money in Cuba in an unauthorised trip there given its embargo if and when they return to the US. The case of this terrorist is even easier from a jurisdictional standpoint. He's a US citizen who decided to instigate hostilities against the US and that's treason and a series of other criminal acts (which also IMO resulted in his loss of citizenship as a collateral civil consequence of his criminal acts) that directly involves the US. It doesn't matter where a person like that is located, or even if they are a US citizen. If, hypothetically, you and I stand on the US-Canada border and start shooting people on the Canadian side from the US side, we are intentionally seeking to injure and kill Canadian citizens and residents in Canada. If we mailed a bomb there, it's the same thing. If we conspired with another person to have them commit atrocities in Canada, it's the same thing. We have chosen to take actions that directly invade, interfere and affect Canada and its territorial sovereignty and its people. Canada is therefore easily within its right to criminalise that behaviour and seek to hold us accountable there for such actions. That's why a guy like Khalid Sheikh Mohammed can be tried in a federal US District Court for loads of crimes relating to him being a mastermind plotter and conspirator in the 9.11 attacks (including but not limited to murder-related counts for each dead victim via co-conspirator and 'felony murder' vicarious liability, etc). That's why Anwar al-Awlaki is likewise liable in US courts for conspiring with the Nigerian attempted bomber regarding the Xmas plane plot. As for Robert Emmet who I cited and you referred above, he would indeed IMO fall under the concept of a bona fide rebel and he's viewed as such today. Ireland was a conquered country, and he was leading an announced rebellion against the country that conquered it. Irish rebels like him followed protocols, rules and patterns of bona fide rebels. As you can see in his trial speech I linked, the British tried to slander him, but he was a bona fide rebel. His brother and Irish rebel, Thomas Addis Emmet, even became a central figure in American Constitutional development after he fled to America, even arguing the landmark Constitutional case of Gibbons v. Ogden. Thomas Addis Emmet - Wikipedia, the free encyclopedia Gibbons v. Ogden - Wikipedia, the free encyclopedia False claims were commonplace in being thrown at many Irish rebels. Take this other example from the trial of rebel John Sheares at his trial for the 1798 United Irishmen rebellion, which was properly announced, uniforms worn, rules of war desired to be followed, etc: The Sheares Brothers - Wikipedia, the free encyclopedia But AQ? They follow the same pattern as the Manson 'family,' Tim McVeigh, the drug and sex trafficker gangs, etc. Their kind of actions are exactly what legitimate rebels like the Emmets and Sheareses themselves would find to be utterly criminal in nature.