Since the end of the eighties, Karel has directed many historical and political documentaries dealing with sensitive subjects of the twentieth century, from the Vel' d'Hiv Roundup (Rafle du Vélodrome d'Hiver) to the Israeli-Arab conflict, while talking about the FMI policy in Jamaica or the extreme right wing in France.
He has also done portraits of French and American politicians – Valéry Giscard d'Estaing, François Mitterrand, Jean-Marie Le Pen, John F. Kennedy and George W. Bush.
In The Empire State Building murders (2008), he combines clips from film noir and recent interviews with actors to tell a narrative story.
He likes to recall François Truffaut's words, "A documentary is one thousand times more of a lie than a fiction, where things are clear from the beginning".
Among them, William chose to include Philip Roth as one of the great American novelists, along with Hemingway, Fitzgerald, Styron, Salinger, Faulkner, Steinbeck and Miller.