[Read: 'ED's Saradha probe in final stages']
According to sources, the CBI is working on leads provided by suspended Trinamool Congress MP Kunal Ghosh who had claimed that Banerjee, along with Trinamool's General Secretary Mukul Roy, met Sen in March 2012 in Kalimpong in Darjeeling during an official visit there.
The MP made those allegations in a CD that he repeatedly released two days after his arrest in November last year. Ghosh, a journalist-turned-politician, was arrested for cheating, breach of trust and criminal conspiracy. Soon after his arrest, Ghosh named 12 people behind the scam on a social media site, and one of them was Mamata Banerjee.
The CBI probe has also revealed lins between the Indian Railway Catering and Tourism Corporation Limited (IRCTC) and the Saradha Group during Banerjee's stint as the railway minister. The IRCTC and Saradha Group firm signed a contract about a tourism project in 2010.