As far as I'm aware they were protesting the fact it was happening at all, and trying to get the police to reform, not to get that one guy in jail.

The protests weren't actually very successful, the aim was police reform and most places didn't see a bunch of police reform.

You could say they were somewhat successful, it certainly got a big chunk of public attention and discussion and debate. However, you need real change, not just chit chat.

The guy ended up in jail after a court case, and the court process always takes months. The courts also do not, ever, listen to things like protesters. They shouldn't.