Paris, July 1942: a thud on an apartment door. It's the French police, come to take away a Jewish family. To try to save her four-year-old brother, Thomas, 10-year-old Sarah locks him in a closet and takes the key with her. In Sarah's Key, a searing film out this weekend, Kristin Scott Thomas plays Julia, a present-day American journalist investigating the family's fate. It's the second feature within a year to tackle the "rafle", the round-up of Jews on 16-17 July 1942 in Paris. What took France so long?

The events are beyond dispute: 13,000 Jews were herded into the indoor cycle track, the Vélodrome d'Hiver. There they were kept for five nights without food or medicine. Of the 10 toilets, five were sealed and most of the rest blocked. There was one tap. From the "Vel" they were taken to the Drancy, near Pithiviers, then to Beaune-la-Rolande prison camps, and thence to Auschwitz. Only 25 returned.

What's made this particularly hard for France to metabolise is that it's a French story. Those enthusiastically carrying out the deportations were French gendarmes. Indeed the rafle depended on the complicity of the French state – not only police but also civil servants, who documented the Jews' whereabouts. The SNCF, the French railway, billed Berlin per head for transport to the German border. And the "Vel" was in the 15th arrondissement, near the Eiffel Tower.

In fact René Bousquet, the French police chief, ordered the round-up of more Jews than the Nazis wanted. (He later helped finance François Mitterrand's presidential campaign.) The order was signed off by Pierre Laval, head of government for the Vichy regime, which passed such virulent anti-Jewish legislation in 1940 that many Jews who fled south after the Nazi invasion soon returned to the occupied north, where conditions were less punitive. Yet when the Nazis finally occupied the southern zone in November 1942, the Italian authorities in charge of the Côte d'Azur refused to deport Jews.

Of course you can't implicate a whole nation. The first European country to give Jews citizenship, France is third in the list of "Righteous among the nations" – the term used by the world documentation centre for the Holocaust, Yad Vashem, for non-Jews who helped Jews. An entire village in the Haute-Loire, led by two Protestant pastors, risked their lives to hide Jews.

Yet the rafle, as Sarah's Key emphasises, was "an event no one wanted to remember", and the tissue of taboo and silence has proved remarkably resilient. With no known images of the round-up, it became an event without a witness. Alain Resnais's film Nuit et Brouillard included a two-second shot of a French policeman outside the barbed wire of Beaune camp. When the film was shown in Cannes in 1955 there was such uproar that the scene had to be excised. Marcel Ophüls's 1971 Le Chagrin et la Pitié provoked similar outrage when it exposed French antisemitism and collaboration. But, curiously, the best film about the Holocaust, Shoah, directed by the French Jew Claude Lanzmann, had nothing to say about the deportation of (in total) 76,000 Jews from France.

While you can't compare French and German responsibility for the Holocaust, some of the differences are instructive. The 1967 publication in Germany of The Inability to Mourn ignited a long, anguished national debate about collective denial, and yet despite a major 1981 book on Vichy and the Jews, it wasn't until 1995 that Jacques Chirac finally acknowledged the culpability of the French state, and then only in response to Jewish and ex-Resistance members' protests. Why has France kept forgetting the deportations, needing to repeatedly remember them?

Perhaps because it involves confronting an antisemitic tradition going back to the Dreyfus affair (and later parallel evasions about Algeria). What's more, the rafle can't be accommodated into France's heroic postwar narrative of a nation of resisters with the odd, bad-apple collaborator. Vichy, they insisted, wasn't part of the republic's history, merely an interregnum.

The testimony of Simone Veil, a government minister and Auschwitz survivor, combined with dogged documentation of complicity by Serge Klarsfeld, have finally helped puncture the taboo, as did the 2004 publication of the novel Suite Française by Irène Némirovsky, who died in Auschwitz. These brought belated recognition that trauma not worked through is passed on, a point Sarah's Key makes by using private secrets to mirror larger social ones. Is France's introduction of five immigration laws in seven years an example of Freud's "return of the repressed"?

History can have a cruel sense of irony. The former site of the "Vel" now houses the ministry of the interior.

• This article was amended on 9 August 2011 to expand and clarify the original sub-heading that said France deported 13,000 Jews.