Italian police have arrested two suspects over the bombing of a school that killed a 16-year-old girl and seriously injured five more teenagers, media reports said here Sunday.
The men were identified from security cameras at the vocational school in the southern city of Brindisi, where the bomb ripped through a group of students as they waited to begin classes early Saturday.
One of the suspects is an ex-soldier with knowledge of electronics, the daily Corriere della Sera reported, citing local news website Brindisireport.
Melissa Bassi died from her injuries in hospital, an only child from a working-class family who was studying to be a social worker.
Another young victim was fighting for her life after suffering extensive injuries to her chest, and another was badly wounded in the legs.
Italy's flags flew at half mast and the Adriatic port city held the first of two days of mourning as Pope Benedict XVI condemned the bombing as "despicable" and said he is praying for Bassi.
Public prosecutor Marco Di Napoli said there was clearly "a wish to carry out a massacre," while playing down speculation that terrorist, foreign or mafia figures could be behind the attack.
"We are far from knowing the truth only 24 hours after" the attack, which has not been claimed, he admitted at a news conference.
"All possibilities remain open," he said, but added: "The most likely hypothesis is that of an individual and isolated act. It's not impossible that it was the work of a single person."
He said police had a photofit of the assailant, whom he described as an "adult man who does not appear to be a foreigner," after security cameras captured "terrible images" of him detonating the bomb.
The person or persons who carried out the attack were familiar with the school's routines and had chosen the precise moment to strike, he said, emphasising that they were "expert at electronics."
"It could be the act of someone at war with the rest of the world or who has psychological problems," he said.
Police have searched the suspects' homes, Corriere reported.
Italy was in shock after the bombing, which revived memories of attacks by political militants and powerful mafia groups.
As people came to the school to lay flowers and attach messages to the perimeter fence, head teacher Angelo Rampino expressed incomprehension over the tragedy. "It the first time in Italy that a school has been attacked. The entire country must rise up. We cannot accept this."
Italian Prime Minister Mario Monti condemned the bombing as tragic and criminal, on the sidelines of the G8 summit in the United States.
The victims were all scorched by the blast, caused by three gas canisters and a timer, with doctors and witnesses describing flying shrapnel and their blackened bodies on the ground.
Thousands of young people spontaneously took to the streets of Italy's main cities in emotional demonstrations against the violence, which many protesters blamed on a rising climate of social tension linked to a severe economic crisis.
The region where the attack took place is a hub of the Sacra Corona Unita (United Sacred Crown), a local mafia that has been under pressure from investigators in recent years and whose influence is seen as being on the wane.
The group, which is heavily involved in drug-running and arms smuggling through the Balkans as well as human trafficking, is believed to be behind a separate bomb attack in the region earlier this month against an anti-mafia campaigner.
Observers pointed to the fact that the school is named after Francesca Morvillo, the wife of famous anti-mafia judge Giovanni Falcone, who was assassinated with her husband and three bodyguards by a mafia bomb 20 years ago on Wednesday.
But officials have cautioned that it is unlikely the Sacra Corona Unita would target civilians in its own territory and said the device used was not sophisticated enough for an organisation that has easy access to explosives.
At a demonstration in Rome on Saturday, several participants said the bombing was reminiscent of attacks carried out by far-right and far-left militants in the 1970s and 1980s in a period known as the "Years of Lead".
Also reviving those memories, an Italian anarchist group claimed responsibility for shooting and wounding Roberto Adinolfi, the head of nuclear energy company Ansaldo Nucleare, earlier this month.
The Informal Anarchist Federation (FAI), has claimed dozens of attacks since 2003 including letter bombing campaigns that have targeted then-European Commission president and Deutsche Bank chief Josef Ackermann.
FAI warned that the shooting of Adinolfi was the first of eight attacks in revenge for the arrest of eight Greek anarchists.