Intelligence officials and police have started questioning a Maharashtra man who offers fresh first-hand testimony on the identities of the Lashkar-e-Taiba commanders who guided the 10-member team that carried out the 26/11 attacks.

Zabiuddin Ansari, who investigators allege was present in the LeT’s control room in Karachi at the time of the attacks, was held by the Delhi Police on his arrival from Riyadh on Monday morning.

In telephone conversations intercepted during the 26/11 attacks, first revealed by The Hindu in February 2010 and now posted online, an individual speaking with a marked Mumbai accent can be heard instructing the terrorists to make a list of demands to the media. The men at the control room also issued instructions to the attack team on operational decisions that included killing of hostages, using voice-over-internet-protocol communications.

Ansari, informed sources said, was held by the Saudi authorities earlier this year while he was travelling on a Pakistani passport, identifying himself as Riasat Ali. In July 2011, New Delhi requested his extradition from Pakistan, as part of a group of more than 50 wanted fugitives.

The arrest, highly placed government sources said, came after months of patient work by the Intelligence Bureau (IB) and Saudi Arabia’s intelligence service, the Ri’asat al-Istikhbarat al-’Amah. Intelligence services in both countries identified Ansari on the basis of intercepted phone communications.

Much of the National Investigation Agency’s firsthand insight into the 26/11 plot has so far relied on the testimony of Pakistani-American jihadist David Headley, who carried out the reconnaissance, which allowed the assault team to reach its targets precisely. He identified Sajid Mir, LeT’s controller of transnational military operations, as one of the men who instructed the team. The Monday’s arrest, government sources said, came after months of painstaking diplomatic talks among the authorities in Riyadh, Washington and New Delhi. Indian dignitaries visiting Saudi Arabia in recent months lobbied the Saudi authorities for assistance in Ansari’s case. IB Director Nehchal Sandhu is also thought to have directly worked with his Saudi counterpart, Prince Muqrin bin Abdul-Aziz, to push forward the investigations.

A Washington-based Indian diplomat told The Hindu that the U.S. used its influence to push forward the case, seeing enhanced India-Saudi Arabia relations as a key element in bringing greater distance in India’s relationship with Iran.

“In the last six months,” a senior official told The Hindu, “Saudi Arabia has dramatically improved its cooperation on counter-terrorism issues with India.”