Rome ( CNN ) -- A man has confessed to planting a bomb that killed a 16-year-old girl and injured five other people outside a school in the southern Italian city of Brindisi , investigators in Italy said . Giovanni Vantaggiato , 68 , told investigators he acted alone in making the device and placing it outside the school , they said . Cataldo Motta , the chief prosecutor for the southern city of Lecce , where the investigation is based , said Thursday in a televised news conference that Vantaggiato had confessed after nine hours of interrogation . He said investigators were still examining Vantaggiato 's motive for the attack , which appeared to be personal , since his explanation was n't convincing . Investigators traced Vantaggiato after examining video that showed him driving his own car and his wife 's car in front of the school in the days before the attack . Police also studied closed-circuit TV footage that they said showed him using a remote control to set off the explosion . He was arrested Wednesday . Vantaggiato , who owns a gas station , had easy access to the gas and gas tanks used in the attack and the know-how to build an explosive device , investigators said . Just after the blast , police found three gas cylinders at the site that were detonated with a remote control , authorities said . The explosion occurred on the morning of May 19 as students were arriving at Francesca Morvillo Falcone school , which offers vocational training . The school is named after the wife of a prominent anti-mafia judge , which fueled initial speculation that the organized crime group might be behind it . Falcone was assassinated in Palermo , Sicily , in May 1992 . Police have since dismissed that theory , Italy 's ANSA news agency reported .
Investigators say Giovanni Vantaggiato confessed to the attack while under questioning . The bombing killed a teenage girl and injured five other people . The device exploded as students arrived for classes at the school in Brindisi .