Yah, 5 ft is point blank with that AR. We can't really see the actual shot, because Rittenhouse was in a cul-de-sac between two cars and Rosenbaum (id not confirmed, but apparently the head shot guy) was between the only camera angle and the shot. Possible he was hit by a ricochet, it was a confined space, and thus did not take any muzzle blast to the head. Certainly on the vid he's breathing and twitching like someone who's just about to expire from a head wound.
Obviously Rittenhouse was running away from the guy who had threatened him earlier. If the DA continues to press the 1st degree murder charge I think the US Attorney should step in and threaten charges on Title 18, U.S.C., Section 242 ( Deprivation of Rights Under Color of Law ) or even the conspiracy enhancement if local officials encouraged it. If there was any coordination with by local officials with the BLM or Antifa groups and there is a traceable link between the people who tried to murder Rittenhouse and the DA, put em all up for a death sentence. After all people died while the police were ordered to stay out of it.