What more can I do about an abusive kindergarden teacher?

My 6 year old son's kindergarten teacher yanked him by the arm and he has a really dark purple bruise which looks like finger marks. I think she probably squeezed when she yanked him. He told me he was getting a drink of water, she told him not to get anymore water when she yanked him away from the water fountain. She complains to me constantly about how many times he washes his hands and goes to the bathroom. She actually has something to complain about everyday. My son has AD-HD, and also might have Asperger's Syndrome so he is very active and curious. It's obvious that my son frustrates her and might get on her nerves. Which is no exuse to ever put her hands on my son or any other student. At the beginning of the school year I pulled him out of that class which is taught by two teachers who had advised me to do so because my son "wasn't ready" and I was so tired of the constant complaining and arguing. I mean, come on, it's kindergarten. What 5 year old doesn't like to play and stay seated without moving around? What 5 year old doesn't ask why for everything? After getting denied entry into a home-school program and after my son turned 6 I had to enroll him back into school. I told the principal, attendance clerk, and receptionist that I did not want my son back in the same class with the same teachers. They told me there wasn't any room in the other classroom and I didn't have a choice. So he went back into the same negative environment and the complaining started right up again. This time instead of arguing with the teacher's I responded by reminding them of his diagnosis and tried to say positive things about my son when they had negative things to say. When my son told me what his teacher did, how he got the bruise, I called the police before I called the school. Two officer's came to my house and had the nerve the ask my son what he did to make his teacher mad! My son told them what he told me and I told them I don't care what my son did, nobody has the right to put their hands on him. I was so upset, I didn't know what to do with myself. The officers left my home to go talk to the teacher at the school and told me to stay put. When they came back they said the teacher admitted telling my son not to get any more water, but denied touching him. The officers said they believed my son, took pictures of his arm, and filled out a report. They told me that she wouldn't be prosecuted because she didn't break his arm. After they left, I went to the school and gave the principal a piece of my mind. She finally put my son in the other classroom, although there is only 3 days of school left, too little too late. I then went to the school district and filed a complaint. They took pictures and told me to take my son to the doctor, urgent care, or hospital and they would pay for it. I just feel like this teacher is getting away with what she did. Is there anything else I can do? My son is scared to go back to school. His teacher hurt him on June 9, I called police and made complaints on June 10. He's supposed to return to school on Monday, June 13. What should I do?