Say, a Russian dissident went a western country, became a citizen, gave up Russian citizenship, then putin visits, this person gets mad, brings a gun and shoots putin.
What will international relations look like? Since the person is not exactly a native of their adopted country. Lets assume trump wasn’t president, what if its a Russian-American? Would the US extradite, or do the trial themselves. Would the headline look like “American Assassinated Putin” or “Russian Dissident Assassinated Putin”. Would it cause more or less tensions, than it it had been a non-russian white person being the assassin?
What about like EU countries? Australia? UK?
Or if the visit was in, say, Japan?
Case by case basis.
So much would depend on the countries involved, and their current relationships.
Let’s say it’s a former Russian citizen who kills Putin in the USA. The new Russian leader might want to have the killer tried in Russia, or they might want to throw the whole thing to the Americans. Legally, if the murder takes place in the USA, it’s the duty of the individual state to deal with it. But if the US President declares it an act of international terrorism, they could push through sending him home.
That’s not even getting into how the murder was done. Putin would have his own security team, plus Secret Service protection, so how did the killer get past them? Was there a conspiracy?
There’s no single answer possible.