The police on the scene say he was bleeding from his face and back of head. After being treated at the scene, he was brought to the station for questioning, at which point, the lead investigator wanted to charge him with manslaughter, but was told not to hold off because the DA/State attorney didn't think there was enough evidence for a conviction.
Further, you have more than one witness allegedly corroborating parts of his story.
This is not to say he isn't guilty or should not eventually be charged, but all of this stands in direct opposition to those who said that the police buried a cut-and-dry case from the start to protect one of their "own".