There's two war-crime issues here.
The first is issuing the death penalty for a crime that -- if it were being committed within American borders -- would NOT be subject to either the death penalty (as a result of due process) or the use of lethal force in the first instance. That is, if these guys were carrying the exact same drugs, except in a truck heading down I-35, it would be illegal to just blow them all up with a Maverick missile from a Predator flying overhead. US law does not allow summary executions of people for simply breaking the law, so long as their actions don't represent an imminent threat to life etc. And precedent is pretty clear that the act of transporting drugs alone is not such an act. Then, even if arrested, charged, and convicted, merely transporting drugs is not a death-penalty eligible offense. SO, the entire approach of murdering people for transporting drugs is a crime.
The second is a sharper issue: as the administration has invoked the laws of combat (however dumb that may be), killing "hors de combat" (sailors floating after you sink their ship is the classic example, actually) is one of the textbook examples of a war crime. Like, it's literally addressed as the Naval Academy as an example of such.
None of the Trump apologists care. Their legal standard is instead "if MY president says they're bad, we should kill them all. Whoever they are." Which is not only depraved, but utterly fucking stupid and short-sighted. Because today, you are on team Trump, and he loves you (he loves the poorly educated). So this is just about extrajudicial killings of THOSE people, not me or MY people. But you forget that in such regimes, it ALWAYS eventually comes around to you and your people.
Sycophants beware. Your turn will come. It always does.