(ANSA) - Genoa, July 24 - Threat letters from self-proclaimed anarchists were sent to the former head of the Ansaldo Nucleare energy firm in the Genoa suburbs on Tuesday. The letter was addressed to Carlo Castellano and signed by the Informal Anarchist Federation (FAI), the same group who took responsibility for the May 7 shooting in the leg of current Ansaldo Nucleare CEO Roberto Adinolfi in Genoa. That attack sparked fears Italy risked seeing a return of the political violence it endured in the 1970s. Castellano, himself shot in the legs by anarchists in 1977, currently heads the biomedical company Esaote, a subsidiary of Ansaldo. Genoa police also received letters signed by FAI on Tuesday and were verifying the credibility of the threats. Authorities last month arrested a number FAI suspects allegedly involved in a series of attacks in an operation that was hailed as a victory for the State. Those arrested are suspected of involvement in numerous attacks, including letter bombs sent last year to Italian tax-collection agency Equitalia, Deutsche Bank in Frankfurt and the Greek Embassy in Paris. However, the investigators said that none of the 10 arrested people were suspected of involvement in the Adinolfi shooting.