17 YEAR OLD SON PUNCHED BY 18 YEAR OLD?

My 17 year old got into a fight with an 18 year old NEAR but not ON his father's property. The other boy punched my son first and then my son hit back just as the other boy's father stepped outside. My son tried to leave but the father (48 years old) basically tried to tackle my son and then his neighbor (probably about 60 years old) came out and helped the father "detain" my son. The father had my son on the ground with his forearm against his throat (leaving a red mark that is still there 3 days later) and the neighbor was holding his legs. The police came and arrested my son but not the other boy. Basically, my son had no witnesses on his side. This family is supposedly our "friends" but the father, instead of calling us (we live right down the street) to come get our son, called the police and they signed a complaint against him for assault. The police asked my son his version but apparently didn't write down what he said, just what the other guy said because the other guy was the one bleeding. I guess they did not pay any attention to the fact that my son had a small welt on his face under his eye where he got punched or to the fact that he had a red mark on his throat from the "adults". We are now going to file a complaint against the boy, the father, and the neighbor. Does anyone know if we have a leg to stand on here?