> I think people only have opinions because of what they have heard from the media.

While I think there is doubtlessly some truth to that, I think it misses the bigger picture which is: People weren't blank slates going into this story. Most people who care about the trial one way or the other already had opinions about subjects relating to the trial before they ever heard of this particular incident. People already had opinions about gun control, self defense, protesting, etc.

Media companies, knowing there are already a bunch of people inclined to feel one way or the other, find it convenient to pander to people with these preformed opinions or biases.