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 wasn'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.