That is the case for so many crimes, perpetrated by all colors and types.
This case was different. Aside from the video, they had multiple witness statements from the defendants themselves that pointed to it being murder. They were convinced, and probably still are, it was self defense. People on their side wanted the video released *to prove their innocence*!
There was a cover up. The reason they weren't charged until after the video wasn't because there was no evidence, but because of cronyism at the very least, or in all likelihood, good ole fashioned racism.