I am no lawyer, and so can't say anything about a legal opinion. But from a "my way of looking at it" perspective: someone who is actively trying to kill american citizens, and is, meanwhile, preventing himself from being tried by hiding in a foreign country should be stopped. Better for all involved if he's stopped without killing, but stopped either way.
I would draw the comparison to someone holding a hostage at gunpoint. You don't put that person on trial before final judgment comes down.
The whole point of trials is to establish that the person performed the crimes that they are alleged to have performed. You can't assume they're guilty and then declare that not holding a trial is OK.
Bob is actively trying to kill Americans and is avoiding trial by hiding in a foreign country. Joe is a peaceful guy who's falsely accused of trying to kill Americans, and lives in a foreign country for unrelated reasons. By what system do you propose we distinguish between Bob and Joe?
I would draw the comparison of someone holding a hostage at gunpoint, so cops go and kill an innocent guy in neighborhood that is pretty much unrelated with the person holding the first as hostage. I'd definitely want to setup a way to judge those incompetent cops.
> someone who is actively trying to kill american citizens
...better have a judgment from a jury, proved beyond a reasonable doubt, after considering the necessary evidence that satisfied any warrant requirements and related rules.
Failure to satisfy this due process - even when the target is a well-known criminal who has fled to another country - could be evidence of the murderer having violated their oath to office. It's certainly not a quality we should allow in our politicians, officers, or civil servants.
/yes, I realize that's not the antecedent for "someone" you intended
I would draw the comparison to someone holding a hostage at gunpoint. You don't put that person on trial before final judgment comes down.