Astonishing!
After long and complicated court proceedings eventually two members of a far right-wing organization were condemned for the deed; Valerio Fioravanti and Francesca Mambro. They maintained their innocence throughout the long court-case and as far as I know have not changed their stance since then. The motive behind the attack remains unclear.
The whole period (mid-70s to mid-80s) is a very murky period in Italian history. Left-wing terrorism, mafia attacks on the civil society, large scale corruption in the police, secret service, among the political sphere, and the growth of far-right extremism almost managed to completely destabilize the Italian democracy.
Several experts see the finger of the Soviet Union in these events (but as you can expect, just as many derides this thesis) and before the election two years ago there was an ongoing parliamentary investigation on the Mitrokhin Archives. This was closed down when Prodi won that election and Berlusconi was forced into opposition.
Here is a link (Wikipedia) to the biography of Robert Fiore. Note that in the article above on the massacre in Bologna it says:
General Pietro Musumeci, n°2 of the SISMI (Military Intelligence and Security Service) and revealed in 1981 to be a member of Propaganda Due (P2), was charged of having created falsified evidence to charge Roberto Fiore and Gabriele Andinolfi, two leaders of Terza Posizione who had fled in exile to London, of the bombing.
The guilt of the two condemned bombers is still debated. Former Italian president Fransesco Cossiga believes in the innocence of Valerio Fioravanti and Francesca Mambro and campaigns for at retrial. His thesis is that the deed was carried out by the palestinian terror organization PFLP, as a revenge for the arrest of one of their leaders, Abu Anzeh Saleh, who had been arrested when trying to smuggle sophisticated Soviet weaponry through Italy.
Three months after Saleh was sentenced a bombing took place in Ustica and a further 5 months later the Bologna massacre. No one claimed responsibility for these attacks.
One interesting piece of information that was revealed during the Mitrokhin investigations was that on the night to the 2 August 1980, two Germans of the RAF (Rote Arme Fraktion - connected to Carlos the Jackal) - Thomas Kram and Christa Frölich -were staying in Bologna. As is well known Carlos had tight connections with the PFLP.
Information exist that Thomas Kram was a "bomb expert". Frölich was arrested a number of years later carrying large amounts of Semtex. She was convicted to 7 years for taking part in the bombing of the train between Marseille and Paris 1982.
Thomas Kram went underground for many years, but last year he and his girl friend, Adrienne Gerhäuser, were arrested by the Germans.
Real nice people, but if they had any connection to the Bologna massacre nothing has been revealed so far.
Militant feminist on trial after 20 years on run
The feminist who fought sexism with fire bombs faces justice