It is very difficult to unearth money trail in such cases of alleged corruption as a lot of ''benami'' transactions take place which are nearly impossible to attribute to a particular individual, they said.
"It was pure luck that we came across these transactions which were done through cheques. These helped us to fit pieces of the jig-saw puzzle," one of the CBI officials said.
The officials said the agency has "so far" not detected any "quid pro quo" in the spectrum allocation scam except the alleged financial transaction between the Kalaignar TV, where Kanimozhi has a 20 per cent stake, and Cineyug but is working on certain leads as investigation is under progress.
A team of CBI officials will be visiting Mauritius which might give an insight into the money trail in the scam and might bring out any bribe money which might have changed hands, sources said.
On the issue of Janta Party President, Subramanian Swamy's claims that agency is ignoring the national security issues in the spectrum allocation scam, officials said "certain" areas concerning national security are being looked into by the agency.
Highly placed sources said in case of corporate lobbyist Niira Radia's alleged role, the agency has found nothing about her involvement in the 2G spectrum scam but she has not yet been cleared and whether she had a role in some "peripheral" issues, like Voltas Land deal, is still being probed.
They said none of the alleged actors of the scam have been given any clean chit and probe is still going on.
Sources said the agency will soon start investigations into the telecom spectrum allocations done during 2001-07 in which it has already registered a preliminary inquiry.