Representatives of India's National Investigating Agency (NIA) questioned the suspects about the bombing on Sunday, two security officials said.
"They are trying to reach out to the top commanders of Jaish-e-Mohammad, including its Kashmir Chief," one of the sources said.
Mohammed Umair, the commander of the Jaish in Kashmir who is believed to have plotted the attack, is suspected to be hiding in the region where the attacks took place, the officials said.
The officials say Umair had "radicalized and motivated" the Kashmiri school dropout who rammed a car laden with explosives into the convoy on Thursday.
Umair is thought to have entered Indian Kashmir from Pakistan in September to head the Jaish in the region. Security forces suspect he is in hiding in southern Kashmir, according to the officials, who could not be named as a matter of policy.