Multi-Disciplinary Monitoring Agency (MDMA) has been investigating the conspiracy behind the killing of Rajiv Gandhi.
It has begun the work of preparing questions that would be sent to Sri Lanka where Padmanathan alias 'KP' is being questioned by the Lankan security, official sources said.
Padmanathan, the alleged financier and a key accused in the Rajiv Gandhi assassination case, was arrested in a Southeast Asian country and brought to Sri Lanka.
The term of MDMA, which is headed by a CBI official and comprises officers from IB, RAW and Revenue Intelligence, ended on May 31, 2009 and was given a post-facto approval.
The investigators want to know the bank details of KP and some more people, including some Indians who were alleged to have hatched the conspiracy to kill Gandhi.
The former prime minister was assassinated on May 21, 1991 when an LTTE suicide bomber blew herself up at an election rally in Tamil Nadu.