He was saying "I can't breath" said it seven or eight times. If you are talking you are breathing, they go hand in hand. The corner say the choke hold was a factor but so was the person kneeling on his back (chest compression) and so was his heart condition. The police did not take him to ground for selling smokes, he was taken to ground because he resisted arrest.
Choke holds are against policy (not the same as being illegal) and the officer should be punished for using it but I have seen no evidence that he intended to harm much less kill Garner. As in most cases where people are injured fighting the police Garner takes some measure of fault for what happened to him. He was very large man and did not go down easy. They could have tased him but with his bad heart the results may have been the same.
We do need to have a discussion about police and community interaction but part of that discussion needs to "if you fight the cops and get hurt is your dumbass fault" and we need to avoid such hyperbole as "black man chocked to death for selling cigerettes"