There’s no universal principle according to which a country can only prosecute crimes commited within its border. Each country decides freely what the juridiction of its courts will be. AFAIK, American courts have a mostly territorial juridiction (apparently with the exception of murder, according to a previous poster). On the other hand, French courts have juridiction for crimes commited in France, or commited by a French citizen anywhere, or when the victim is a French citizen, again, regardless of where the crime has been commited. In fact, France never extradites its own citizens (with some exceptions within the EU) but prosecute them herself. So, in the example you gave, yes, the culprit could be prosecuted in France. But if the murderer was, say, a Russian, it’s possible that Russia couldn’t prosecute him because its courts have only a territotial juridiction (I don’t know if they do, that’s just a random example).
And nothing prevents a country to make special exceptions to its general principles for specific crimes. For instance, at some point, Belgium claimed universal juridiction for crimes against humanity (even for instance if the crime was commited by an Australian in Zambia against a Nepalese citizen). As a result,complaints coming from everywhere piled up in Belgium. In the particular case of sex crimes against minors, both the USA and France made special exceptions. Already explained in the case of the USA, and in the case of France, by allowing prosecution even if it wasn’t a crime in the country where it happened (usually, it needs to be a crime in both countries for France to prosecute acts commited on foreign soil)
My brother had a Canadian diplomatic posting (to the USA). The Foreign Affairs department made sure he carefully understood the consequences of anything he did that would attract the attention of the authorities in Washington… basically, “yes it’s a Get Out of Jail Free card, but if you need it, or any of your family you will be very sorry when you get home.” The Canadians don’t tolerate the sort of privilege abuse one reads about for, for example, third world UN diplomats in Manhattan abusing their positions. This wasn’t even about underage girls, it was about anything. And, it wasn’t because they thought he was going to do anything interesting, but because they wanted to be sure he understood the responsibility.
I assume the same goes for anyone going off to work for a government agency in a foreign land, immunity or not - here are the rules, here’s the problem if you break them.
IIRC, there is some international law of the sea treaty, based on historical precedents - where basically piracy on the high seas (arrrgh!) can be prosecuted by whatever jurisdiction catches the perps, so the concept of extraterritoriality has a long history, and for very good reason - protection of anyone who is at risk.
That’s odd, I know when I was in the military they told us the military age of consent was 16, presumably that would apply regardless of where the soldier was stationed, unless local law proscribed a higher age.
Exactly. If they heard about this kind of crap happening, they would likely send the guy home and have him look for work when he gets there.
There was an incident with a Russian diplomat who killed someone while DUI in Ottawa, then departed for Russia and Russia declined to waive his immunity. Canada does not appreciate abusing the position.