Syed Zabiuddin Ansari, an Indian Muslim from Maharashtra who was recently deported from Saudi Arabia allegedly told investigators he had taught Hindi to the ten attackers and given them tips on how to dress like typical young Mumbaikars.
He is believed to have joined the Lashkar e Taiba group which carried out the attacks.
The LeT began as a militant group fighting to end Indian rule in Jammu and Kashmir, but it has since grown to become a global terrorist organisation with close ties to al-Qaeda.
It is believed to have been used by Pakistan's security forces as a proxy for attacks on Indian troops in Kashmir.
Indian frustration over the lack of progress in Pakistan's investigation into the Mumbai attacks has been muted recently, but it surfaced again yesterday when Foreign Secretary Ranjan Mathai said Islamabad should do more if relations are to make progress.
"I emphasised that terrorism is the biggest threat to peace and security in the region and that bringing the guilty to justice in the Mumbai terror attacks would be the biggest confidence-building measure of all," he said.
His counterpart Jalil Abbas Jilani however rejected Indian claims of state complicity. Islamabad is however "willing to enter comprehensive co-operation in order to defeat the forces of terrorism," he said.
