NEW DELHI // The voice had long haunted Indian police investigating Mumbai's deadly 2008 terrorist attack.
They had repeatedly listened to recordings of mobile phone intercepts containing chilling words from one of the men who guided 10 terrorists through the gun rampage that killed 166 people in India's financial capital.
"Pass this message to the media: 'This is just the trailer. The real film is yet to come,'" the voice said.
Anti-terrorism officers engaged in one of India's largest investigations had no idea who the man was, only that he had a Mumbai accent and used Hindi words, which was unusual for Urdu speakers such as the attackers on the ground.
Now, police believe they finally have the man behind the voice. They ferreted out their suspect from Saudi Arabia where he was hiding, according to officials close to the investigation. They said he had given himself away to the police by opening a Facebook account under his real name - Syed Zabiuddin Ansari.
Mr Ansari - an Indian citizen whose aliases include Abu Humza, Abu Jindal and Abu Jundal - was arrested at New Delhi airport on June 21 after Saudi Arabia agreed to hand him to Indian officials and put him on a flight home.
Indian investigators said that Mr Ansari was considered a key player in the Pakistan-based Islamic terror group Lashkar-e-Taiba's plans for attacks on India. They believe he was so central to the Mumbai attack plans he was among those giving orders by the minute to the attackers or directing them on their mobile phones from a control room in Karachi, Pakistan during the November 26-28 bloodbath.
The investigators spoke on condition of anonymity because they were disclosing sensitive information.
Mr Ansari's interrogation is expected to bolster the Indian government's accusations - and accepted as a fact by most ordinary Indians - that Pakistan was behind the attack, the most brazen terrorist operation on India's soil. His arrest is a rare piece of good news for a government reeling from economic and political troubles.
"Clearly there was state support for the 26/11 massacre," Home Minister Palaniappan Chidambaram said on Friday.
Indian investigators say Mr Ansari has already told them that Pakistani intelligence officials were in the control room during the 60-hour siege - corroborating testimony by American terrorist suspect David Coleman Headley, who said during his Chicago trial last year that Pakistani Inter-Services Intelligence officials were involved.
Ansari has also told investigators he fled India in 2006 across the border to Bangladesh, escaping from a police raid in the western Indian town of Aurangabad on an illegal cache of weapons and explosives intended for future attacks within India, the officials said.
Mr Ansari then moved to Pakistan, trained with Lashkar and joined in planning future attacks, officials said, speaking on condition of anonymity because of the sensitivity of the case.
Pakistan insists that the ISI, as its intelligence agency is known, has no links to Lashkar, and denies any connection to the Mumbai attacks.
The assault was like no other India had experienced. Bombs and grenades went off at the famed Taj Mahal and Trident hotels. Then, 10 trained Pakistani militants fanned out through the hotels and through the main train station and a Jewish cultural center and gunned down people in their paths.
The attack went on for three days, as Indian police scrambled to keep up with the militants who were receiving detailed instructions by mobile phone.
Eventually all but one of the gunmen were killed. The survivor, Ajmal Kasab, told a special Indian court he and the others were tutored by a man named Abu Jindal on how to speak with a Hindi accent to avoid detection in India and confuse police about their origins.
Investigators had been looking for Mr Ansari for years after he was implicated by other suspects in the Mumbai attacks, but they never knew his exact role in the attack, said officials close to the investigation.
India learned Mr Ansari was living in Saudi Arabia on a Pakistani passport, officials said.
Both India and Pakistan then began lobbying for his release into their custody, but India clinched the arrest by providing DNA samples from Ansari's Indian family members, who live in the western state of Maharashtra, where Mumbai is located, the officials said.
Intelligence agents are now interrogating Mr Ansari in a secret location on the outskirts of New Delhi.
Mr Ansari told Indian investigators he had gone to Saudi Arabia on Lashkar's orders to raise funds and recruit more Indians as militants.
He might have remained in the shadows had he not opened a Facebook account in his real name to find new recruits, the officials said. The Times of India reported last week that Mr Ansari also used the account to contact Lashkar accomplices, who may have been under global scrutiny by intelligence agencies.
Indian investigators followed his electronic trail to Riyadh, and this week used voice recognition tests to match Mr Ansari's voice with the man on the tape. While the Hindi he spoke is similar enough to Urdu that speakers understand each other, there are many words that differ.
The man recorded giving instructions to the attackers used a few Hindi words an Urdu speaker would not use, such as "prashasan" for "administration", officials said. The Urdu word would be "intizamiya".
Investigators have sent the voice samples to a lab for further analysis, newspaper reports said.
Saudi Arabia's decision to hand Mr Ansari over to India, rather than Pakistan, appeared to surprise Indian officials. Saudi Arabia and Pakistan have long held close ties.
Foreign Ministry spokesman Syed Akbaruddin described the arrest as something "rather new" in Saudi-Indian relations. "Our relationship with Saudi Arabia is expanding in a variety of ways."
Analysts said Riyadh's decision marked a significant shift.
"It is a signal to Pakistan that it will get isolated if it thinks state sponsorship of terrorism can be a viable policy option," said Ajit Doval, former chief of India's Intelligence Bureau.