Information is still incomplete. There are probably bits here that will piss off people on both sides. :-/
First, I've seen no evidence that Rittenhouse was a white supremacist. He was clearly a police and militia fan, probably destined for a career in police work. With violence erupting in Kenosha, he saw an opportunity to realize some of his dreams, helping the cops keep violence under control.
He reportedly told bystanders before the shooting that he was there to keep order and to provide medical help to protesters if needed. So as far as his mental state going in, I don't see much hint of racism or white supremacy. I see a naive 17 year old with a deadly weapon, jumping into an already confused setting. I don't see any reason to believe that he was looking to kill anyone; more likely he wanted to be a hero.
The cops that night are hard to understand. In a tense situation, those untrained, loosely organized and heavily armed militias and vigilantes roaming the streets are a catalyst for disaster. The police thanking them for being there (instead of asking them to get off the street), sharing water and chatting...really hard to understand. It's not clear to me if Kenosha was under a curfew that night. If so, I don't understand the cops not sending the militias home or arresting them.
One militia/vigilante type claimed on video before the shootings that the cops had told them that they (the cops) would drive the protesters down to them, and then leave, because they (the vigilantes) knew how to handle them. That could be taken several ways - confidence in their peace-keeping abilities, or a wink-wink-nudge to do what feel like with the protesters. Of course, this is all second hand, we don't know what the police actually said, if anything.
FIRST SHOOTING
Somehow, an altercation started. Rosenbaum was chasing Rittenhouse, throwing objects at him. Rittenhouse stopped and shot Rosenbaum an unknown number of times (maybe one? maybe multiple?), with at least one shot in the head.
Seconds later Rittenhouse walked up to see Rosenbaum's condition. Some shouted to call 911. Rittenhouse made a phone call. People started shouting that Rittenhouse had shot someone, and began chasing. Rittenhouse began running, and can be heard saying "I shot somebody". It isn't known who he was talking to. If it's 911, that says a lot about his state of mind and intentions. If it's a militia contact or friend, that's a bad sign.
Rittenhouse runs. The police radio has a description of him (white male, green shirt, long rifle), his location and direction.
He trips, and several apparently unarmed protesters attempt to jump on him. (There are still frames that may show a handgun in one of their hands, but that's ambiguous and there's no indication yet that anyone shot at Rittenhouse. Also fairly strange to suggest that a person with a handgun aimed at a fallen person with a rifle would choose to jump on him rather than shoot...) One of the pursuers was carrying a skateboard, possibly to use as a weapon...or maybe just to not lose it.
In the seconds that follow, two more are shot, one fatally. Rittenhouse gets up and continues down the street. Several more bursts of gunfire are heard as Rittenhouse is backing up with the rifle, it isn't clear if he's shooting again or if the shots are coming from elsewhere.
He continues up the street, and police vehicles arrive. He is in their headlights, carrying a rifle, hands up...a white man in a green shirt and a long rifle as described over the radio. People are shouting to the cops that he shot people. Multiple police vehicles pass Rittenhouse, who leaves and returns to Illinois.
Things are still confused. Key questions remain: how many shots did he fire, who did he call after the first shooting, what exactly were his motivations for being there, how did the first altercation start?
But some things are clear. Having that many people carrying weapons in a crowd creates exponentially more chances for something to turn deadly. Having that many people with weapons out makes it almost impossible for the police to identify threats when a shooting happens.
I haven't yet seen any sign that Rittenhouse's motivations were anything worse that being a naive police fan-boy looking for a chance to be a hero. His first shooting was a wildly disproportionate escalation of violence by a panicked kid who was in a situation way over his head. His running from the first scene may be a perfectly rational response to a mob chasing him, his decision to open fire a second time was another reckless escalation.
My take-away so far? This is the kind of thing that is likely to happen if you have a large number of armed people in a tense situation. Arguments are guaranteed to happen. Pushing, shoving, spitting, probably some punching are all likely. But when frightened people with guns are in the mix, homicides become the likely outcome, and with enough guns, the police have an extremely confusing environment when the shooting starts.
At this stage, I haven't seen evidence that supports a 1st degree homicide conviction. I see some terribly bad decisions that raised the risk needlessly, and a panicked gunman who decided to shoot to avoid the possibility of a beating, and did it again moments later as the situation escalated.
Interesting takes on "gun populism" vs. "gun militarism" in the police. It explains a lot of what happened.
https://www.vox.com/2020/8/27/21404117/kenosha-kyle-rittenhouse-police-gun-populism
https://www.theonion.com/blue-lives-matter-supporters-say-kyle-rittenhouse-not-r-1844869225