 How much preparation remains unclear. FBI uses the term flash to bang. They are looking into the planning, including how long it was. It could have been just the day before the rally and whether their trips to the site to scope a vantage point to shoot. Investigators believe at this point that the shooter named Thomas Matthew Crooks acted alone, but they are continuing to investigate whether someone may have accompanied him to the rally. That's one reason why they are seeking eyewitnesses and videos.