The CBI will soon send a formal request to Switzerland to help the agency in tracking down the alleged money trail of Swan Telecom , a company chargesheeted in the allocation of 2G spectrum.

CBI sources said this was decided after documents received from Mauritius indicated flow of money to other European countries considered as tax havens.

They said Letters Rogatory (LR) will be sent to Switzerland authorities to share investigation details in the allotment of second generation spectrum in 2008.

"We have received ownership patterns and details of investments by a number of companies based in Mauritius. Prima facie it appears that funds have been routed to Switzerland through some channels. We are still examining all documents and will send our team to probe it," a CBI official said.

Mauritius-based front companies of foreign investors are often utilised as a route to avoid paying taxes in India.

The sources in the investigating agency said the CBI has asked details of Mauritius-based Delphi Investments Limited, Murphy Investments Ltd, Capital Global Ltd, Black Lion Ltd, Inditel Holdings, Deccan Asian Infrastructure, Aidetel Holding, Kaif Investments, Electro Investments Ltd and Palab investments for their alleged role in the 2G scam.