Riyaz Bhatkal had suggested adopting tactics used in the 2013 Maoist attack on Congress leaders in Chhattisgarh to kill politicians.
The National Investigation Agency (NIA) said this in its supplementary charge sheet filed before a special court.
Home Ministry is exploring the possibility of lodging case under Unlawful Activities Prevention Act.
His parents and siblings in Colombo are yet to contact the Indian authorities over his arrest.
The accused, identified as Arun Selvarajan (28), is wanted in Sri Lanka for allegedly sheltering an LTTE cadre.
The accused, identified as Arun Selvaraj, allegedly disguised himself as an event manager.
British deputy PM Nick Clegg, whose focus was mainly economic, education and climate change, was extremely impressed by PM Modi.
After police arrested the main accused in Gandhi Maidan blasts, Indian Mujahideen had been planning to carry out blasts.
Congress chief spokesman K K Mishra alleged the NIA had changed the theory to suit its present political masters.
Under the MLAT, either country can approach the other for collecting evidence against an accused.
The NIA claimed that one of the motives for the murder was the “sexual advances’’ made by Joshi.
NIA’s special prosecutor Subhash Bhattacharya told The Indian Express that the agency asked for time and the court granted it.
The hearing of the tribunal at Port Blair is scheduled for July 20 and 21.
As per the petition, there was an inordinate delay in the investigation.
Rohatgi had represented the Italian govt at the legal proceedings during UPA-II tenure.