CBI sources said the agency has despatched Letters Rogatory for details of financial transactions, meetings of alleged middlemen and their interests in Indian and Tunisian companies, among others.
The top executives of Italian firm Finmeccanica and its United Kingdom-based subsidiary AgustaWestland are facing trial in Italy for alleged corruption in supply of 12 VVIP helicopters to India.
The INR 3600-crore contract is also under probe of Indian agencies for alleged kickbacks paid to Indian officials, including former IAF chief S P Tyagi, to clinch it.
The alleged bribes were routed through a company with subsidiaries in Tunisia and Mauritius, the sources said.
Tyagi has denied allegations of any kickbacks.
Giuseppe Orsi and Bruno Spagnolini, former and current Chief Executives of AgustaWestland respectively, are facing trial in Italy for alleged corruption.
Orsi was heading AgustaWestland when the deal was signed in 2010 and is now the Chief Executive Officer of parent company Finmeccanica.
The statements of both these top executives are important for CBI for finalising its charges which would be levelled in the charge sheet, the sources said.
India has become a civil party in the ongoing trial in Italy which helped it in getting court documents submitted by Italian prosecutors in connection with the case.