Gabriele Sandri, 26, a Lazio fan heading for a Serie A game in Milan, died at motorway rest station Sunday morning when an officer fired warning shots to stop a clash between fans of Lazio and Juventus, who appeared to have met by chance near the Tuscany town of Arezzo.
The fan's death triggered violent reactions in Bergamo and Rome, where hundred of fans clashed with police Sunday night.
Inter Milan-Lazio was the only game cancelled Sunday afternoon, but Atalanta hooligans in Bergamo caused their club's home game with AC Milan to be abandoned after using a manhole cover to destroy a glass barrier and by threatening to invade the pitch. Five other Serie A game were played regularly.
Authorities decided to cancel the late game between Roma and Cagliari, which was already considered at risk, but riots began outside the Stadio Olimpico where hooligans attacked city policemen, damaged cars and motorcycles and set fire to a police bus.
Later in the night, nearby police offices and the headquarters of the Italian Olympic Committee (CONI) were attacked by hundreds of people.
ANSA reported that nine policemen, three photographers and dozens of hooligans were injured in Rome.
La Gazzetta dello Sport reported that groups of hooligans in Milan threw stones at a police office and confronted officers outside the headquarters of the state television RAI.
Violence took place also in the southern town of Taranto, where fans of the lower-division side caused the interruption of the game with Massese.
Slogans against the police were chanted in several stadiums, often comparing the death of the Lazio fan to the killing of a policeman in clashes outside the stadium of Catania last February.
La Gazzetta Monday carried the headline "What a nightmare!" on its front page, while Il Corriere della Sera published an interview with the police officer who accidentally fired the fatal bullet.
"I aimed at no one. I was at least 200 metres away, how could I (take aim)?" the officer said.
"I fired a first shot in the air. The second went off as I was running, damn myself. I know I am ruined now. I destroyed two families, the boy's and mine."
It appears that his police patrol had stopped at a rest station across from the one where fans were clashing and that it was impossible for the officers to cross the motorway.
The policeman, who was identified only as Luigi S., fired a shot and ran trying to read the number plate of the cars of the fans who were leaving the rest station.
Interior Minister Giuliano Amato said the killing was "a tragic error, but it happened in circumstances linked to the violence that permeates football and every week forces thousands of agents to patrol cities and roads to prevent that the worst happens."
As investigations continued, reactions and comments hinged on the decision taken by police authorities not to suspend the whole round of games Sunday and on how to curb football-related violence.
"Personally, I would have suspended (all) the games, but I cannot tell if it would have been a valid choice for public order," said Fausto Bertinotti, president of the parliament's chamber of deputies.
Police national chief Antonio Manganelli, who appears to have decided that the games had to be played while football authorities asked to suspend them, said that "the police will take their own responsibilities (for the alleged killing)."
Suggestions of a possible suspension of the league were put on hold Monday morning by Giancarlo Abete, president of the Italian football federation (FIGC).