As many as 139 cases were being investigated by the government's Serious Fraud Investigation Office (SFIO) in last three years until April 20, Finance and Corporate Affairs Minister Arun Jaitley said on Friday.The SFIO has probed nine cases in 2015-16 so far and 56 were referred in the whole of the last fiscal, Jaitley told the Lok Sabha in a written reply. In 2013-14, a total of 63 cases were investigated.In a separate written reply, Jaitley said over 30,000 prosecutions have been filed and a total of Rs.2.71 crore fine imposed in the last three financial years and the current fiscal till April 20.The SFIO has filed 230 complaints at different forums during the last three financial years, he added."During this period, in respect of the cases filed by SFIO, conviction has been made in 12 cases wherein fine of approximately Rs.3 crore have been imposed. In six cases, directors of the company concerned have been sentenced to imprisonment for six months," Jaitley said.