President Obama's recent visit to India brought up a sore point with many Indians: the question of David Coleman Headley, a Pakistani American who has confessed to involvement in the deadly 2008 attacks in Mumbai.
Many Indians think U.S. officials are not telling all they know about the shadowy figure who worked for both the U.S. government and terrorists based in Pakistan.
Headley was arrested in Chicago in October 2009 and charged with planning terrorist attacks in India and Denmark.
He has since confessed to scouting targets for the Pakistan-based Lashkar-e-Taiba militant group, responsible for the Mumbai attacks, which left more than 160 people dead, including six Americans.
For many Indians, those attacks have the same emotional resonance as the Sept. 11, 2001, attacks have for Americans.
But the U.S. agencies that arrested Headley didn't tell the Indian government about their catch until some three months later.
About the same time, the Indian news media got wind of the story, says Siddharth Varadarajan, bureau chief of The Hindu newspaper in New Delhi. He has been covering the story since it broke.
Headley, who had been convicted on drug charges in the United States in the 1990s, had received an early release from prison so that he could serve as an informer for the U.S. Drug Enforcement Administration.
Headley made several trips to Pakistan, apparently to report on drug trafficking. In many ways, he must have seemed perfect for the assignment.
He was born in Washington, D.C., in 1960, the son of a Pakistani father and an American mother. Then, his name was Daood Sayed Gilani.
After his parents divorced, he grew up in Pakistan, where he attended an elite military academy. Later, as a teenager, he returned to live with his mother in Philadelphia, where she operated a bar called The Khyber Pass.
In 2005, he anglicized his first name and adopted his mother's family names, a move that removed any hint of his Pakistani ancestry from his American passport. That made it easier to gain entry to India.
FBI Disregarded Warnings
What makes Indians so angry is that U.S. agencies had warnings that Headley had links to the anti-India terrorist group Lashkar-e-Taiba.
"The DEA may have heard stories about what he was doing," Varadarajan says. "One of Headley's wives may have complained to the FBI that this guy, apart from beating her, was also involved with Lashkar-e-Taiba."
A tip from Headley's American wife reportedly made its way to the FBI's Joint Terrorism Task Force, but was apparently shelved for lack of evidence. Varadarajan says U.S. agencies apparently didn't share that information, either among themselves or with Indian intelligence.
Another of Headley's wives, a Moroccan woman, told U.S. embassy officials in Islamabad, Pakistan, that she believed her husband was a terrorist plotter, but her warning, too, was apparently disregarded.
In a statement to the New York Times this month, an unnamed senior U.S. official said an investigation concluded that there wasn't enough evidence at the time to act on the warnings, or to pass them on to India.
"David Coleman Headley is just a tip of that iceberg," says Ved Marwah, a retired New Delhi police commissioner who served in all of India's trouble spots during the course of his career.
Marwah, who was also an intelligence officer, expresses the widespread Indian belief that Pakistan's government, its military and its intelligence service, the ISI, are deeply involved in supporting anti-India groups such as Lashkar-e-Taiba.
He says the United States has long ignored India's warnings about these connections, in part because the U.S. government was angling for Pakistan's support for the war in Afghanistan.
"But here again I think America is making a huge mistake," Marwah says. "They were wrong earlier, and they are wrong now. Because if they think that the Pakistani army can be persuaded, not pressurized, to change its course, they are in for a huge surprise."
Marwah says he thinks Pakistan will continue to support terrorists like Headley and that the U.S. must share intelligence information with India to prevent further attacks.
Pakistan denies any involvement in the attacks and says it has cooperated in the investigation.
U.S. officials did give Indian intelligence agents a chance to interrogate Headley as he was being held in Chicago, but only three months after he had been arrested.
Varadarajan, the journalist, says that raised the perception that U.S. intelligence officials feared that Headley could reveal too much about Pakistani involvement.
"They realized that the information Headley has will implicate the Inter-Services Intelligence, the Pakistani intelligence agency, to a much higher degree than what might be politically comfortable for America," Varadarajan says.
For that reason, he adds, Indians suspect they may never know the whole truth.