You think they are planting evidence on a random citizen in the most high profile murder case in years? Why does that seem unthinkable to you? The shooter riled up the richest and most powerful class in the most powerful country in the world. Ask yourself if you truly believe the authorities would be content with we have no suspect and no leads for a prolonged period of time, even if that were legitimately the case? They would never allow the perception that someone could do that and get away with it.