(ANSA) - Rome, September 26 - The offices of Rome's mass transit company ATAC and two other firms were searched on Wednesday in connection to an alleged half-million euros in kickbacks in exchange for buying 40 city buses. The other two companies searched were bus manufacturer BredaMenarinibus, owned by Italian defence and engineering giant Finmeccanica, and Eur, a property management company joint owned by the State and the city of Rome. ATAC is suspected of accepting 500,000 euros in bribes in return for ordering 20 million euros in buses for the city in 2009. Prosecutors have placed four suspects under investigation, including Eur CEO Riccardo Mancini and the former CEO of BredaMenarinibus, Roberto Ceraudo. ATAC was probed last year on suspicion of abetting easy hirings of relatives and friends of Rome politicians.