If the FBI provides these voice samples, the investigators will compare them with the tapes -- of the 26/11 terrorists's telephonic interactions with their minders during the attacks -- which are in the Mumbai police's possession.
This comparision will help the agencies establish if Headley and Rana were briefed the terrorists during the attacks.
Intelligence sources say they have considerable evidence that show the duo had contacts with the Lashkar-e-Tayiba personnel who carried out the attacks. But the bigger question -- if they guided the 10 men on the ground with the help of satellite phones -- will become clear only after the investigators get the voice samples from the FBI.
Meanwhile, the investigators have been able to ascertain that Headley possessed a satellite phone when he visited New Delhi for the first time on March 7, 2008. Sources say he could not have smuggled the equipment, but was provided the instrument by a local contact in the capital.
"We are yet to verify if he used the same phone during all his visits to India or he changed the phone frequently. It is clear he would have stayed in touch with his Pakistan handlers with the help of the satellite phone," the sources said.
There is no evidence, the sources added, that Headley picked up the phone from the Pakistan embassy.
Headley's Pune connection will also be put under the scanner. The staff at the Surya Villa hotel -- where he reportedly stayed -- will be questioned about his activities in the city. The Osho ashram, which he twice visited, is close to the Chabad House in Pune. The Chabad House in Mumbai was attacked during the November 26 attacks; the rabbi, his pregnant wife and several guests at the Jewish centre were killed by the terrorists.