On the trail of Pakistani terror group's elusive mastermind behind the Mumbai siege

Two years later, Mir and his victims are at the center of a wrenching national security dilemma confronting the Obama administration. The question, simply put, is whether the larger interests of the United States in maintaining good relations with Pakistan will permit Mir and other suspects to get away with one of the most devastating terrorist attacks in recent history.

For five months, ProPublica has examined the investigation of the attacks and previous cases documenting the rise of Lashkar. This account is based on interviews with more than two dozen law enforcement, intelligence and diplomatic officials from the United States, India, Pakistan, France, Britain, Australia and Israel, including front-line investigators. ProPublica also interviewed associates and relatives of suspects and victims who had not discussed the case with journalists and reviewed foreign and U.S. case files, some of them previously undisclosed.

These documents and interviews paint the fullest portrait yet of the mysterious Mir, whose global trail traces Lashkar's evolution. His name has surfaced in investigations on four continents, his web reaching as far as suburban Virginia. Fleeting glimpses of him appear in case files and communications intercepts. A French court even convicted him in absentia in 2007. But he remains free and dangerous, according to U.S. and Indian officials.

ProPublica's investigation leads to another disturbing revelation: Despite isolated voices of concern, for years the U.S. intelligence community was slow to focus on Lashkar and detect the extent of its determination to strike Western targets. Some officials admit that counterterrorism agencies grasped the dimensions of the threat only after the Mumbai attacks.

The FBI investigation into the killings of the Americans has focused on a half-dozen accused masterminds who are still at large: Mir, top Lashkar chiefs and a man thought to be a major in Pakistan's Inter-Services Intelligence Directorate (ISI). U.S. officials say Washington has urged Islamabad to arrest the suspects.

"We put consistent pressure on the Pakistanis to deal with Lashkar and do so at the highest levels," said the senior U.S. counterterrorism official. "There has been no lack of clarity in our message."

But U.S. officials acknowledge that the response has been insufficient. The effort to bring to justice the masterminds - under a U.S. law that makes terrorist attacks against Americans overseas a crime - faces obstacles. A U.S. prosecution could implicate Pakistani military chiefs who, at minimum, have allowed Lashkar to operate freely. U.S. pressure on Pakistan to confront both the military and Lashkar could damage counterterrorism efforts.

"It's a balancing act," a high-ranking U.S. law enforcement official said. "We can only push so far. It's very political. Sajid Mir is too powerful for them to go after. Too well-connected. We need the Pakistanis to go after the Taliban and al-Qaeda."

Pakistani officials said they had no information on Mir. They denied allegations that the powerful ISI supports Lashkar.

"Allegations of ISI's cadres operating in connivance with the militants . . . are based on malicious intent," said a senior Pakistani official who spoke on the condition of anonymity because of the issue's sensitivity. ISI "remains top-to-bottom transparent and rests under the complete control of the civilian government . . . There is no question that the government thinks that all militants are enemies of the state."

A year ago, Pakistan charged Lashkar's military chief and six less-influential suspects in the Mumbai attacks. But the trial soon stalled over legal complications and conflict with India, raising fears among U.S. and Indian officials that the prosecution will collapse in a court system that rarely convicts accused extremists.

"It didn't matter why the war was going to happen," testified Kwon, a Virginia Tech graduate who had worked at Sprint. "The only thing that mattered is that our brothers and sisters in Afghanistan needs [sic] help against imminent attack."

The Virginia jihadis joined up in Lahore at a Lashkar office decorated with posters depicting the U.S. Capitol in flames and the slogan: "Yesterday we saw Russia disintegrate, then India, next we see America and Israel burning."

Mir soon cleared the volunteers to train for holy war.