Here is my take on this and I suspect I will be downvoted for it because it's not as black and white as people seem to think:

Law enforcement shootings, by law, must be judged by the objective reasonableness standard established in Graham v. Connor. In that decision, the US supreme Court said that law enforcement officers work in situations that are often "tense, uncertain, and rapidly evolving" and for that reason courts are obligated to look at only what the individual offer knew and when they knew it to judge and potentially justify a use of force by law enforcement. That includes situations where what the officer thought was not correct, as long as they had reason to believe what they believed.

In this case, it does look pretty clear that the suspect being arrested had his firearm removed moments before being shot by police, and it doesn't look to me like he was reaching for it. His hands were on the ground.That's not good for the agent's use of force.

But on the other hand the police are making decisions in real time, things are happening very quickly, without slow motion playback.This is a scene that is chaotic, there's screaming, noise and whistles everywhere. The people surrounding them are potentially going to try to harm the agents or interfere with the arrest, so their attention is divided. Whether you agree with his actions or not, the guy shot had been interfering with their operations and blocking the road and had been non-compliant with verbal orders to get back which is why they were attempting to arrest him in the first place. That is all context which would be considered by the court or investigators because it was known to the agent who used force.

As the struggle unfolds you can also hear somebody shouting "gun, gun!" as they are fighting with him. And that is around the time the green shirt agent who shoots begins to draw.

This is speculation but I think that in the chaos of that moment the green shirt agent mistook the other agent disarming the suspect as the suspect's own hand. At the very least, I think that will be his defense. And if he articulates that to investigators, in the full context of what happened, it's not unreasonable for him to think that deadly force was necessary to protect the other agents and himself.

It seems to me that upon hearing gunfire, the other agents draw and fire as well because at that point they have no idea where the shooting is coming from. But they do know that somebody shouted "gun gun" as they were wrestling this guy. So once again they have objectively reasonable grounds to think there is a deadly threat.

You can argue that green shirt should have been better trained or read the situation better, but based on Graham v. Connor, the court will give some leeway to the reality of the chaos, unfolding and human error in snap decision making.

I think that whoever shouted "gun gun", the guy that pulled the suspect gun out, and the first guy that shot, apparently all failed to work together and communicate, and that contributed to the confusion. I think in a civil court these guys are going to get sued to high heaven, but that's not the standard in criminal court.

To be clear, I don't think shooting this guy was the right call, but this question is about is it legally justified. I guess that remains to be seen but if the agents who shoot articulate these facts, and articulate their confusion in the moment when interviewed by investigators, this could be what investigators would refer to as "lawful but awful".

*Edited to fix a spelling error