Former AC Milan midfielder Gennaro Gattuso,one of the key players in Italys World Cup-winning team in 2006,was placed under investigation for match-fixing on Tuesday as an inquiry into football corruption targeted Milans last title campaign. Four others were arrested in an early morning police sweep. Cremona prosecutor Roberto Di Martino,who has been leading the Last Bet operation for three years,told The Associated Press that Gattuso and retired Milan and Lazio player Cristian Brocchi were allegedly part of a ring that fixed Serie A and other Italian matches at the end of the 2010-11 season. About 30 matches,a good part of them involving Serie A,are under investigation, Di Martino told the AP. Gattuso said he was angry and offended. This stuff is absurd and incredible, Gattuso told SportMediaset TV. I dont even know what it means to fix a match,I wouldnt know where to start. Lets see what happens now but Im certain that everything will be cleared up. Brocchis agent,Davide Lippi,said his client was innocent. The four people arrested on Tuesday were Salvatore Spadaro,Francesco Bazzani,Cosimo Rinci and Fabio Quadri. Each of them allegedly helped connect fixers to players,Di Martino said of the case that has seen more than 50 people arrested since mid-2011. Di Martino said a couple of the people arrested met as recently as this year,suggesting matches continue to be fixed. Were seeing clear facts that despite the arrests and investigations a good part of these people continue to do what they did before, Di Martino said later in a news conference,lamenting that past arrests have not made much of an impact. There certainly were not big reactions in Italy,considering that things continue to go on like before. CRIMINAL ASSOCIATION Gattuso and Brocchi face charges of criminal association with the aim of fraud and sports fraud,and had their homes searched. About 20 other people were also placed under investigation. Gattuso and Brocchi were connected to the case by the use of phone taps,Di Martino said. Gattuso,who won two Champions League titles with Milan,was fired as Palermo coach in September. Brocchi is coaching in AC Milans youth program. Police said in a statement that the arrests were carried out in Milan,Bologna,Rimini and Messina. Other former and current players placed under investigation included Claudio Bellucci,Davide Bombardini,Leonardo Colucci,Lorenzo DAnna,Nicola Mingazzini,Claudio Terzi,Samuele Olivi and Fabrizio Grillo. The Gazzetta dello Sport reported that Milan matches against Lazio,Chievo Verona and Bari in February and March 2011 were under investigation,plus games against Juventus and Inter Milan. Milan won its last title in 2011. LAST BET operation The last Bet operation has resulted in more than 100 people placed under investigation in Italy since mid-2011,with suspect matches being looked at by prosecutors in Cremona,Bari and Naples. The case has led to lengthy bans for former Lazio captains Giuseppe Signori and Stefano Mauri,as well as former Atalanta captain Cristiano Doni. Several clubs have also had points deducted. Prosecutors have detailed an extensive match-fixing ring stretching as far as Singapore and South America that was allegedly in operation for more than 10 years. The arrests of 14 people in Singapore in September was hailed as a major breakthrough in the fight against corruption in football. The Last Bet operation came only a few years after the 2006 Italian match-fixing scandal,which revealed arrangements with referees and resulted in Juventus being stripped of the 2005 and 2006 Serie A titles.