The "innocent until proven guilty" bit is refering to the opinion that should be held by a juror, not to facts in the world. Were I a juror I would require that his guilt be proven. As I'm in the role of a reader of an article about it, I cannot take the same stance, lest I not have an opinion about anything.
Yes, it *IS* the task of a court, and in particular of a jury, to decide legal guilt. But legal guilt is not actual guilt, and, in fact, often gets things wrong. (Not, however, as often as a biased and illegally acting police officer.)
To the police he should have been a suspect. They apparently murdered him. But even this, alone, would not have set off a civil disturbance. That is clear evidence that this is a part of a pattern of behavior on the part of the police such that the community believed them to be habitually violent thugs biased against the community. (It's not proof, but only strong evidence, that this is an actuality.)