Eventually the official narrative was formed by the FBI. According to this story, Aaron Alexis went to the fourth floor and then fired below at coworkers in the atrium, likely targeting those he had issues with at work. Above is a CBS animation of this. Many witnesses have stated that he fired from this location.
A timeline issued by the FBI shows Alexis started the rampage on the building’s fourth floor and then moved down to the third and first floors. He ultimately returned to the third floor, where he was killed around 9:25 a.m. FBI Director James Comey has said there’s no evidence that Alexis shot down into the atrium despite earlier accounts from witnesses at the scene.
“We have not determined there to be any previous relationship between Alexis and any of the victims,” she [Valerie Parlave, assistant director of the FBI field office in Washington] said. “There is no evidence or information at this point that indicates he targeted anyone he worked for or worked with. We do not see any one event as triggering this attack.”
Everyone knows that the media makes mistakes. This is not an issue of that. However, they have sourced an entire narrative to federal law enforcement authorities and eyewitnesses, only to have the former replace that version of events almost entirely. That isn't confusion or incompetence - it's a cover-up, and it's in the open for all to see.