I don't know if it could have been prevented by arresting just this murderer, as it's far from an isolated incident.
I do however think it could have been prevented by an edict from the top years ago, issuing a zero-tolerance policy for harassment, abuse and murder by police officers, with focus on clearly racially motivated incidents. I'm fom the UK, so don't claim to understand american politics, but I just don't understand why something like that hasn't happened, especially when Obama was president.