“Very few things,” United States counter-terrorism official David Benjamin said in a recent speech, “worry me as much as the strength and ambition of the Lashkar-e-Taiba.” The arrest of Pakistani-American jihadist David Headley, alleged to have carried out the reconnaissance that enabled a ten-man assault team to kill over 160 people in Mumbai last November, could prove a significant step forward in delivering justice to the victims of the horrific attack. But the arrest has also underlined the reach of the Lashkar’s transnational networks, which give South Asia’s most dangerous jihadist group global lethality. British-born Dhiren Bharot, held in 2005 for attempted bombings in the U.S., had trained with the Lashkar and fought with it in Jammu and Kashmir. French national Willie Brigitte, held for planning terrorist attacks in Australia, was another product of the Lashkar’s transnational operations. Lebanese national Assem Hammoud, held in April 2006 for planning to target Port Authority Trans-Hudson commuter trains running between New Jersey and New York, was preparing to travel to Pakistan to acquire the expertise he needed to do so. And just this week, five Washington, D.C. men were picked up in Sargodha, Punjab, where they had travelled to acquire military training.

Sadly, policy-makers across the world have been muddled in their responses to the threat. Like all violent crime, terrorism rests on two pillars: the intention to carry out terrorist acts, and the capabilities needed to do so. That the Federal Bureau of Investigation believes it arrested Mr. Headley on the eve of another attack in India demonstrates that Islamabad lacks either the influence or the will to rein in the Lashkar. The threat will remain until Pakistan finally acts to eliminate Lashkar capabilities, in the form of its training camps, recruiting tools, and finances. In the wake of the November attacks, Pakistan promised the United Nations Security Council that it would proscribe the Jamaat-ud-Dawa, the Lashkar’s parent organisation. It is yet to do so. Mr. Headley’s upcoming trial on 12 terrorism-related charges, including the murder of six U.S. nationals in the Mumbai attacks, will cast substantial new light on the planning and conception of the carnage. The American trial is also likely to proceed with un-Indian speed. India would do well to facilitate the rapid progress of these legal proceedings, and to focus its investigative resources on discovering whether elements of the network, of which Mr. Headley was a part, are still active here. The wider challenge for New Delhi will be persuading the world to work with it to compel Islamabad to give up its rationalisation of inaction and deliver on its promise to dismantle the infrastructure of terror.

More In: Editorial | Opinion