Mr Andreotti, 80, is charged with being the mandante, issuing the orders for the 1979 killing of Mino Pecorelli, a muck-raking journalist with close connections to the Italian secret services.
The prosecution argues that Mr Andreotti wanted the journalist eliminated to prevent publication of incriminating information. As the editor of a magazine of political scandal Mr Pecorelli was preparing to publish material on the Italcasse financial scandal. In a cover story entitled "The President's Cheques" he intended to denounce Mr Andreotti for drawing money from a government-owned bank to bail out friends in difficulty.
Also, Pecorelli planned to publish a copy of a memorial written by the slain Christian Democrat leader, Aldo Moro, during his kidnapping by the Red Brigades. Mr Andreotti was Prime Minister at the time of the kidnapping and, according to Mr Pecorelli, Moro realised he was being abandoned by his party because of his call for an "historic compromise" with the Communist Party.
Much of the prosecution case is based on the testimony of pentiti, former mafiosi now living under police protection programmes. Defence lawyers say the pentiti are unreliable and ready to endorse the investigators' hypotheses in return for reductions in their own prison terms. The likelihood of Italy's foremost post- war politician going to jail is remote. If he were convicted, he could still appeal to two higher courts, a process that normally takes about ten years.
But Mr Andreotti's judicial Calvary does not finish in Perugia. He is also on trial in the Sicilian capital, Palermo, in a case that has far- reaching implications for Italy's entire political system. He is charged with associazione mafiosa, complicity with the Sicilian Mafia, Cosa Nostra. Those proceedings are also expected to finish late this month or in early October. The prosecution has asked that he be given a 15-year term and be banned from public office for life.