That was 1000% preventable. You don't get to kill people based on circumstantial evidence without even counting the number of bystanders, without verifying their identity, without doing any level of human intelligence, all easily accomplished tasks, and then claim that you did everything you could.
It's absolutely clear the US did not give a single shit about civilians. Many US and coalition soldiers were even happy to kill civilians. You don't authorize a policy of systematically killing first responders ("double tap strikes") and then claim you were trying to minimize civilians casualties. It wasn't a mistake, it was knowingly just not giving a shit.
It's clear where stand: "Things happen in war"
https://en.m.wikipedia.org/wiki/United_States_and_the_Intern...
But I would think murder war crime implies intent not negligence.
The two(+) that are perhaps the most relevant are those that provided the intelligence (framing), and those that made the decision to act on it.
[0] I don't know how much liberty drone operators have to make live decisions in the .. "field" about whether to engage or not, but I suspect this case involved some level of abstraction.
If there were a massive amount of charges filed for everyone involved with the strike, I'd agree that the servicemen should also be charged. I'm not sure that's where we should start, as I feel it's too likely that's also where we would end and they are the least responsible of the related parties.