India, July 14 -- Evidence collected by the Federal Bureau of Investigation (FBI), including intercepted conversations and emails between Tahawwur Rana, David Coleman Headley and Lashkar-e-Taiba (LeT) planners in Pakistan, forms the key basis of conspiracy charges filed earlier this week by the National Investigation Agency's (NIA) in the 26/11 Mumbai attacks, according to officials familiar with the development.

The federal agency on Wednesday filed a supplementary charge sheet calling the Pakistani-born Canadian citizen a "key conspirator" based on his interrogation and evidence collected, both by it and the FBI, which was also part of extradition documents.

For instance, the FBI recorded a conversation between Headley and Rana when t...