As the first camcorder-ready terrorist act of the rolling-news era, the attacks of 11 September 2001 were rooted so fully in visual spectacle that it feels as if 9/11: the Movie has always been with us. That might explain why few narrative film-makers have broached the events of that day.
With the exception of Paul Greengrass's United 93, which is set on-board the only one of the four hijacked planes not to reach its target, and Oliver Stone's World Trade Center, about two Port Authority police officers trapped in the rubble of the twin towers, there has been a general reluctance on the part of narrative cinema to reshape material that exists already in the collective memory.
Asked where we were when the planes hit the towers, many of us are able honestly to reply: "I was watching."
The challenge of competing with images that most viewers will have intimate recall of is not insurmountable. United 93, a highly effective thriller, has the opposite effect of most action cinema: it encourages a suspension of belief, rather than disbelief, enabling the audience to forget temporarily that a happy ending is out of the question.
I suspect that time will judge United 93 harshly. It will look increasingly naive, even government-friendly. In 2006, however, it was the film that needed to be made, not least to wrest the lion's share of power away from the terrorists (who are shown being attacked by a number of the passengers). Once other film-makers have developed more sophisticated responses, United 93 and World Trade Center will be considered test runs - the first pancakes thrown away before the batch proper.
That said, Stone's picture cleverly withholds the familiar in its own way. Instead of adopting the wide shot favoured by news channels, the film shows only the shadow of a low-flying plane plunging a street in Manhattan into darkness, accompanied by a terrifying whoosh. Viewers are faced with the exotic experience of understatement in an Oliver Stone film.
And while Michael Moore's Fahrenheit 9/11 is a documentary - and therefore exempt from some of the pitfalls facing a predominantly imaginative interpretation - it offers a lesson to all film-makers in the business of restoring shock. In Moore's picture, the attacks on the twin towers are played in sound only against a black screen. Cinema audiences were forced to fill in the blanks themselves, while the auditorium's darkness evoked the closed eyes of prayer or contemplation.
If the feeling persists that no one has yet made the film about 11 September 2001 that we are waiting to see, then, perhaps, the truth is that there isn't one to be made. Or maybe it is already out there, comprised of fleeting moments from many different movies that some enterprising curator or editor will eventually get around to compiling. The emergence early on of two portmanteau films - 11'09"01, featuring shorts by different directors, and the documentary Underground Zero - seemed to imply that the subject is too large for any one director.
Plenty of film-makers have approached the terrorist attacks obliquely or sideways-on, as though they were a Medusa-like creature that could only be regarded via the reflection in a shield. Pictures such as Reign Over Me (about a man who loses his wife and child in the attacks) and My Name Is Khan (a Bollywood film in which a man with Asperger's syndrome travels to the US in the aftermath of the attacks to tell the president that he is not a terrorist) use that day as a springboard for other storylines. Stephen Daldry's forthcoming adaptation of Jonathan Safran Foer's novel Extremely Loud and Incredibly Close will no doubt inhabit the same territory.
In the 2010 romantic drama Remember Me, directed by Allen Coulter, the attacks loom ahead of one character and foreshorten his life. There is a risk of exploitation in any work that makes use of the event in this way, relegating it to the level of a plot twist. Yet you could argue that such a tactic is true to the nature of what was an arbitrary atrocity, at least from the perspectives of the victims.
While film has largely shied away from depicting the attacks, ripples from them continue to spread outwards. No one assembling a season entitled "Cinema After 9/11" would have any trouble filling a month's programming slots: from the docudrama of The Road to Guantánamo - a film about the Tipton Three by Michael Winterbottom and Mat Whitecross - and Antonia Bird's The Hamburg Cell, which imagines the hijackers' preparations for the attacks, to the satire of Team America: World Police, the dystopian science fiction of Children of Men and the liberal wish-fulfilment of The Visitor, 9/11 casts long shadows.
Those shadows reach into Spike Lee's 25th Hour and Inside Man, and even into period pieces such as Martin Scorsese's Gangs of New York and Steven Spielberg's Munich, both of which end with shots of those eerily flawless columns on the skyline.
What the cinema of 9/11 is missing transparently is the equivalent of the taboo hypothesis proposed by Neil LaBute's play The Mercy Seat, in which a businessman is with his lover when he should be at his office in the twin towers on 11 September 2001; knowing that his family will presume that he has perished, he considers beginning a new life. That kind of imaginative leap hasn't yet been made in film.
Five years ago, I suggested that we would eventually see a comedy based around the attacks and this would be a symbolic liberation. It's true that Chris Morris's black comedy Four Lions was inspired, in part, by the London bombings of 7 July 2005. Richard Curtis uses a strategic mention of the twin towers in the prologue of Love Actually to provide a cynical transfusion of gravitas. And Morgan Spurlock piggybacked on the headlines in his facile documentary Where in the World Is Osama Bin Laden? Still, no director has tackled 9/11 with anything other than solemnity.
What, you might reasonably ask, is there to laugh about? I remember news anchors on the day of the attacks struggling to find an adequate tone in their commentary; the flustered attempts of superficial personalities to reflect fully the gravity of the situation certainly felt grimly humorous to me. "The World Trade Center," reflected one broadcaster surveying the scene. "Yes, it really was a centre for world trade." Isn't there the germ of a new, abrasive Broadcast News in that somewhere?
If an unspoken aim of film-making about the attacks of 11 September 2001 is to deny terrorists the final story credit, defiant comedy is surely one of the sharpest weapons at our disposal. The outrage that has greeted stand-up routines about 9/11 delivered by comics such as Joan Rivers and Gilbert Gottfried suggests that it will stay sheathed for some time to come.