NEW DELHI (AP) - India's top investigative agency has filed a criminal case against a former air force chief and 12 other men on charges of cheating and conspiracy in a US$750 million (S$934 million) helicopter deal marred by bribery.

The Central Bureau of Investigation (CBI) on Wednesday filed the charges against Shashi Tyagi, three of his cousins and four defence companies after investigations revealed that bribes were paid to steer the contract to Italian defence group Finmeccanica's helicopter division, AgustaWestland.

The CBI is India's equivalent of the US Federal Bureau of Investigation. The agency searched the homes and offices of the 13 men who it says received bribes to clinch the purchase of 12 helicopters two years ago. India's defence ministry received three of the helicopters in December but has placed the rest of the contract on hold.