(ANSA) - Rome, July 19 - The gray areas surrounding the death of anti-mafia magistrate Paolo Borsellino represent a "humiliation" for the Italian State, Italian president Giorgio Napolitano said on the 20th anniversary of Borsellino's murder on Thursday. "It is a humiliation for all of us who represent the democratic state!" the president wrote in a statement, responding to a letter from Borsellino's widow in which she said she will spend the rest of her life trying to understand the motives behind her husband's death. "We are working on it, and we must work without rest and hesitation, in order to reveal and punish the errors and disgraces that have polluted our understanding of the massacre," he added. Many of the mobsters involved in the 1992 killings of Borsellino and fellow anti-mafia magistrate Giovanni Falcone have been brought to justice, including former Cosa Nostra head Salvatore Riina, who ordered them and a number of bomb attacks in Rome and Florence. But many shadows continue to hang over this period in Italy's history. These include doubts about whether politicians were involved in negotiations with the mafia at the time and whether rogue elements in the nation's secret services had a role in the bloodshed. Napolitano himself has recently been linked to investigations into allged negotiations to stop the series of Cosa Nostra bomb attacks that claimed the lives of Falcone and Borsellino, but the head of state denies this.