Updated

A bomb blast outside a high school in southern Italy that killed a 16-year-old student has revived dark memories of the 70s and 80s, when terrorists, anarchists and organized crime carried out dozens of bloody attacks across the country.

Investigators had no firm clue Sunday of who was behind the attack and there was still no claim of responsibility a day after the crude device made up of gas cylinders exploded outside a mainly all-girls vocational school in the Adriatic port town of Brindisi.

The blast could be the work of an individual "angry with the world" said the prosecutor heading the investigation, Marco Dinapoli.

"It is not impossible that a person acting alone did all the organization," he said, adding that the person would have needed some weapons training to assemble the device and set it off by remote control.

The prosecutor indicated that a nearby closed-circuit security camera had captured images of the alleged attacker.

An anti-Mafia magistrate, Cataldo Motta, said Saturday that although it didn't appear that local organized crime gangs were behind the attack, it was too early to reach conclusions.

Killed in the blast was Melissa Bassi, who friends say dreamed of becoming a fashion designer. The condition of four other young women, all schoolmates and hospitalized with burns, was reported Sunday to be improving.

The mainly all-girls Francesca Laura Morvillo Falcone vocational institute is named after a judge who was killed alongside her prosecutor husband, anti-Mafia hero Giovanni Falcone, in a highway bombing in Sicily, exactly 20 years ago, leading some to think the mob may be responsible.

Interior Minister Anna Maria Cancellieri, in charge of domestic security, said she was "struck" by the fact that the school was named after the judge, but she cautioned that investigators at that point had "no elements" to blame the school attack on organized crime.

The bombing follows a spate of recent attacks against Italian officials and government or public buildings by a group of anarchists, including the shooting and wounding of an official from a nuclear engineering firm, which is part of a state-controlled company. An anti-nuclear anarchist group that previously had targeted Italy's tax collection agency claimed responsibility for the shooting.

The attacks and threats lodged against authorities prompted the government on Friday to assign bodyguards to 550 individuals, and deploy 16,000 law enforcement officers nationwide.

"But you can't militarize the country," the interior minister said.

Italy coped with a severe terrorism outbreak in the 1970s and 1980s — known as the "years of lead." In the worst attack, blamed on right-wing terrorists, 85 people were killed in a bomb blast at the Bologna train station in 1980. A Mafia terror campaign targeted churches and public buildings in Rome and Milan.

Corrriere della Sera, Italy's leading newspaper, said the government and investigators needed answers as soon as possible to avoid the country reliving the "fantasy of the strategy of tension."