Due to the massive wide-scale happenings it would've been almost impossible for the firemen to make elements of that particular documentary, fictional. It does contain bias however because it shows you it from the perspective of the firemen/cameramen only and they incorporate their own feelings and emotions because they can't speak for everyone else who was in New York at the time. Editing techniques, narration and music though, evoke certain emotions from the viewers. Missing some scenes out may have been necessary to prevent any graphic, offensive or disturbing material from being shown and so, it does manipulate the outcome. Classical and ambient music was used at certain intervals, usually when there were extreme high-angle long shots of the rubble of the two towers - indicating the destructive aftermath. There was a huge contrast between the camera action and what appeared in frame from the fireman's perspectives of using his own hand-held camera, to the opening and closing sequences made by the more professional film company - shooting Robert de Niro and his on-screen narration for example. This therefore distorted the truth of the situation by implying that the chaos was over, when really it may have just shifted to a new form such as trying to search for people among the rubble.
It is obvious that certain decisions were made about this documentary, especially amongst the scripted narration and opening and ending narrative sequences and shots. As stated, it is extremely biased and could even have been shown as a form of propaganda to show how evil the alleged terrorists were and so support for the "War on Terror" would escalate, whether it was justified or not.
Nick Broomfield is well-known for his controversial documentaries, such as "Aileen Wuornos - The Life & Death of a Serial Killer" and "Biggie and Tupac". Broomfield believes that "fictional films are trying to imitate reality, while documentaries are reality!" In the documentaries I have watched of his, I have noticed that he often keeps a neutral stance in certain situations, which is often the best policy, so as to avoid bias and warping of truths.