(ANSA) - Rome, October 22 - Italy's supreme Court of Cassation found, in a ruling filed Tuesday, that a missile was the definite cause of a mysterious airplane crash more than three decades ago near the Sicilian island of Ustica. On June 27, 1980, an Itavia airlines DC9 commercial liner plunged into the sea while flying from Bologna to Palermo, killing 81 people in a disaster known in Italy as the Ustica Massacre. The court ruling mandates a new civil trial to assess the responsibility of the Italian defense and transport ministries in Itavia's bankruptcy. The petition for the trial was made by Luisa Davanzali, the heir to Aldo Davanzali, who owned Itavia. The Italian high court ruling said that the hypothesis that the plane was downed in 1980 by a "missile shot by an unknown airplane" appears "by now consecrated" even "in case law". The statement was making reference to a Court of Cassation decision in January that gave final approval to 1.2 million euros in compensation for three families who lost loved ones in crash. Italy's top court in January found that it was caused by a missile fired in error at the passenger liner. The top court ruling, which faulted civil and military radar systems, was the first definitive sentence since criminal proceedings were inconclusive. The court said the State must pay damages to all 81 victims' families for failing to ensure the safety of the skies - an order challenged in June by the state attorney general, who said the ruling was not based on facts and called for a new civil trial. However, Italy's highest court on Tuesday found that "cover-ups" in investigations into the Ustica plane disaster must now be considered "definitively ascertained". A middle appeals court had rejected Davanzali's request for a civil trial seeking damages from the State, despite acknowledging botched investigations. The Cassation Court on Tuesday rejected the middle court finding, saying that the court "errs" by excluding "the possible effectiveness of cover-up activities" and its effect on the airline's collapse. The private commercial airline went bankrupt six months after the plane disaster.