The French held significant influence within the old Rwandan (Hutu nationalist) Government who went on to commit Genocide. At any point in the month long massacre that killed nearly a million people they could have put their foot down in order to, at the very least, tamp down some of the killing. Going beyond inaction, there have been an abundance of accusations that France actively participated by shuttling Hutu nationalist to cities, villages, or dwellings where Tutsi (or moderate Hutu) citizens were hiding and subsequently murdered. As the Genocide began to slow down and the RPF (Rwandan Patriotic Front, the rebel army who fought the Hutu Nationalist government both before and after the Genocide) began to gain control, the French helped to evacuate many of the genocidaire's (mostly of upper government position) out of Rwanda and into the DRC or abroad. The French were some of the first on the ground in the DRC to provide aid and create refuge encampments for the fleeing Hutu Nationalist who were now on the run after having murdered their neighbors. The French media blasted on about the dangerous RPF and the poor Hutu who were fleeing an unprovoked army who wanted them dead for no reason; don't mind the million dead Tutsi and Hutu brothers and sisters those Hutu Nationalist left behind them. And the reason for it all, essentially, is because French policy was to side with whoever spoke French. That's it. Seriously. They just didn't care about what was happening and they desperately wanted to keep French speaking leadership in control.

Check out the Wiki on Rwanda and do some source clicks, it has plenty of places to start on this topic, but really you need to find books and media written about the subject, of which several good ones have been mentioned in these comments.

EDIT: further to add, the French being found "complicit" is not the same as the French being found responsible (what you wrote). They helped further the cause of genocide in ways that go beyond simple inaction (inaction being the flavor of diplomacy the rest of the world adopted). The Hutu nationalist are the ones ultimately responsible and no one denies that, but while the rest of the world turned a blind eye the French were doing deals with the devil under the table.