It's almost a pop culture proverb that if someone is accused of something sensational, say, kiddie-diddlin', the accusations will be trumpeted on the front page, and if those accusations turn out to be false, the retraction is below the fold on pg. 23 with the dry-cleaning coupons and right before the obits.
Similarly when you see this and this, understand that it's because the media raced each other to the six o'clock news to report the most fabulous version of events as provided by biased witnesses. I'd be willing to bet that a majority of the people in those photos are protesting a teenager getting shot in the back, a narrative not remotely supported by the facts, but trumpeted by the news enough that it has become fact for the people in question.
In a world where a 300lb man wrestling for a cop's gun is consistently referred to as an "unarmed teenager" while a man with a pen knife that never left his pocket is always referred to as an "armed man", it's hard not to believe there's more than a little bit of truth to claims of a "narrative". If some Ferguson business owner were to sue the big news organizations for the damages... well, I'd love to be on that jury.