I'll try and make my position absolutely clear. I'd like you to watch the video again, and really tell me if you think there even was an opportunity for anyone to help.
For the first 28 seconds of the video the officer has things mostly under control. At around 28 seconds, he actually is able to take both hands off the guy and look away for a second to put something in his pocket. At that time the person filming actually makes what turns out to be an accurate comment. He says "that's a very aggressive stance". Aggression would be right. For the next 15 seconds or so, he again, still has things mostly under control. He is on top. The guy isn't doing anything threatening. It does indeed appear he is not able to cuff him, however at the moment, the guy still isn't doing much. At 51 seconds the cop appears to knee him in the head. At this time the guy starts to defend himself by getting to his knees and holding on to the cop. The both go to the ground. Now he begins to fight back, gains the upper hand, and starts socking him in the face. At this point the cop shoots.
There was no time for intervention. There was no need for intervention by a bystander until 61 seconds into the video. The shots came at 71 seconds.
Had they tried to help, they would have likely got there at around the time he shot, putting their own lives at risk.
When could they have helped?
Why couldn't the cop retained the position he was in for the first 30 seconds, when no struggling was going on?
I'm not second guessing him shooting. I am suggesting that had he not escalated the situation at around 51 seconds, he not only wouldn't have needed the bystanders help, but he wouldn't have needed to shoot.
What is wrong with me suggesting that? What makes suggesting the bystanders should have helped any different?