Angry residents of the southern Italian city of Brindisi say they are anxious to know who carried out a blast that killed a 16-year-old girl and injured 10 others.
The bomb went off in front of the Morvillo-Falcone high school as some students were going into class on Saturday morning.
Italian media reported a possible a mafia link. The school is named after an anti-Mafia prosecutor who was assassinated 20 years ago.
But officials say the unsophisticated device and the target of an all-girls school does not point to organised crime.
The man leading the investigation thinks the blast was probably an isolated act and says officials are reviewing video evidence from the scene.
On Saturday evening, residents paid tribute to Melissa Bassi who died in hospital from injuries sustained in the blast.
One resident said: “I hope it was not an act of terrorism. Any other option would be much more acceptable.”