You be the judge: "Saint Omer"

Saint Omer marks the French filmmaker Alice Diop's transition into full-length fiction from acclaimed documentaries, and you can tell. For the last 105 of its 122 minutes, Diop's latest project offers a soup-to-nuts account of a trial held in the market town of the title, centred on a Senegalese student, Laurence Coly (Guslagie Malanda), who's been accused of murdering her 15-month-old daughter. Yet this courtroom drama is prefixed by an unusual prologue introducing us to Rama (Kayije Kagame), an academic looking on at the trial from the gallery. Diop shares a lot of information here that doesn't initially seem all that relevant from a narrative perspective: what Rama is teaching (Marguerite Duras, how female collaborators were treated after WW2), dramas within her family, what she saw out the window of the train that took her to Saint Omer, even what she does with her hotel bedlinen. As is apparent from the small handful of less than glowing reviews of Diop's film, one response to this scene-setting might be a restless "get on with it". What becomes clear is that this is Diop showing her working - as modern documentarists are encouraged to do - because it turns out she, like Rama, sat in on a real-life trial of this kind, and found herself negotiating certain issues as events played out before her. The film's insistently frontal framing represents an attempt on Diop's part to bring a renewed honesty and transparency to cinematic fiction - to meet the audience on the level, and from the off try and show exactly where everybody on screen is coming from.

This is important, because the case under discussion is an odd one, at once open-and-shut and far more complex besides. In a move typical of the upfront approach, Diop has her judge (Valérie Dréville) lay out the established facts in an early monologue for jurors and viewers alike. The dead infant was left to drown on a beach; after initially denying culpability, Laurence copped to the crime; and now, finally, here we all are. In her opening remarks, the accused maintains she has no clue what drove her to this heinous act, instead expressing a sincere hope the trial (the French procès feels more resonant in the context) will illuminate her motives; she then pleads not guilty. The implication is that there may well be extenuating circumstances, not unlike the extenuating circumstances that prologue entered on Rama's behalf. Thereafter, the uncluttered clarity of Diop's blocking and framing underlines the parallels between these two women. Both have spent time thinking about crimes and punishments. Both have issues with their extended family: in Laurence's case, she believes someone put the evil eye on her. Both are alert to the sore spots of race and gender that flare up during the trial, and such is the fierce directness of this camera that we too become attuned or reattuned to them: the all-white jury, the child's father - a befuddled older fellow - ducking out of taking responsibility for pre-natal care because "men didn't do that sort of thing in [his] day", the blithe racism of Laurence's PhD supervisor, who wonders why an African student would have any interest in an Austrian philosopher like Wittgenstein. Here, as elsewhere in Saint Omer, you can almost literally feel the air being sucked out of the courtroom; what Diop must have realised, sitting up in the gallery, is that a trial can recreate the perfect storm of indifference and insensitivity that leaves people in handcuffs and lives hanging in the balance.

She counters that indifference with thoughtful presentation; this isn't just a lesson in citizenship, but a richly rewarding lesson in film style. Saint Omer immediately distinguishes itself from movie norms by setting us down in the middle of the calmest, least fractious courtroom in screen history, overseen by a judge who barely raises her voice - it is a place, crucially, where you can hear yourself think. What you often find yourself thinking about, when you're not busy mulling the particulars of this case, is the assurance and elegance of Diop's camera set-ups. Laurence's testimony, to isolate one element, is recorded in a single medium shot, with no movement to stir false action, nor straining close-ups at moments of high emotion. Diop displays a documentarist's readiness and determination to let her camera run - to hear out her subjects without distraction, allowing them in turn to underline or undermine their own account of themselves. When the framing is this simple (by narrative cinema standards), any subsequent reframing - and any shift in the judicial balance - registers as doubly potent. There's an astonishingly effective (and suggestive) sequence late on in the trial, where we observe Rama zoning out as two white barristers argue among themselves on the topic of female genital mutilation; just by the sheer drift of its camera, the film shows us someone becoming alienated from language itself, in a way that might have inspired Wittgenstein to fill several more volumes. And yet the movement connects the characters, and connects those characters to the audience. Rama knows how Laurence feels; we know how Rama feels; ergo, we know how Laurence feels, in as much as anyone can ever truly know how anybody else feels.

Far from superfluous, then, that initial framing story represents the run-up in the leap of empathy Diop wants us to take: Rama is another of those onlookers who arrived horrified by this crime and then came to consider the plight of the accused, to walk a mile in shackled shoes. This is where, for all its perspectival clarity, Saint Omer gets actively tricky: it's a film offering a retrial to someone who was found legally culpable, so as to determine whether or not she can also be considered morally and spiritually culpable. Parsing that may require our reaching an understanding - uncomfortable as the process might be - that the circumstances as presented here meant the victim stood even less chance than the woman who rather shruggingly carried her into this world. When Laurence confronts the prosecution lawyer with the freighted question "So why did I do it?", she's asking everyone - Rama, the jury, those of us in the cheap seats - and there aren't easy answers, let alone comforting ones. At least one onlooker has arrived at the conclusion Saint Omer may represent the year's best advert for infanticide, but this is surely to overlook the implications of the film's closing images, which return Rama to everyday life, and show her persisting in the face of the horrors the trial brings up. There is still hope, but perhaps it now has to be cultivated from within. Diop, with her documentary grounding, trusts we can handle the truth - jagged, incendiary, awful though it often is. Saint Omer, the first great film of 2023, serves as its own kind of evidentiary proof - not least that the notion of a cinema for adults, a cinema of ideas and emotions, isn't as dead as we might have feared.

Saint Omer opens from today in selected cinemas.