Can they still charge my son even if they already verified the real shooter?

I'm in Chicago, on Oct 31 2013 my 17 year old son was taken arrest and release to me. A girl got hurt in the eye with a BB gun after school. The police came to my home to arrest my son, they claim there was a witness that saw him and another boy shooting. They also arrested the other suspect. After questioning both kids (which requested to be present and was not allowed even though my child is a minor). The detective’s stated his going to send the case to the judge. Even though they found the other boy was the one to be the shooter using the BB gun. And stated my son was not even at the scene when the incident happened. But the girl states my son was there (but not sure). And according to the detective she was okay. What should I do before going to court? My son never had been in trouble. How would this affect his record? Should I get a lawyer? Why did they charge my son after the boy clearly said he was not there and same story was told by other students. Please what should I do? I’m very worried.