For Pakistanis, the Dec. 27 assassination of Benazir Bhutto was the J.F.K. murder and 9/11 rolled into one, plunging the nation into days of mourning and setting off riots across the country. It was a stunning victory for Pakistan's militants, who have increasingly turned their firepower against the state, conducting more than 50 suicide attacks in 2007 alone.

The government quickly fingered Baitullah Mehsud as the mastermind of the Bhutto assassination; he had previously threatened to kill her. The details of Mehsud's biography are sketchy, as he shuns publicity. He is known to be in his mid-30s and to lead thousands of militants, many of them Mehsud tribesmen, in Waziristan, a tribal region on Pakistan's border with Afghanistan.

In his first television interview, conducted by al-Jazeera last year, Mehsud said his ultimate aim is to attack New York City and London. This was more than mere rhetoric. In January, Spanish police said a cell of Pakistanis they arrested in Barcelona were planning suicide operations in Spain and possibly elsewhere in Europe. They had allegedly been dispatched by Mehsud. And so we can add another name to the list of Islamist terrorists with global reach.

For the moment, the Pakistani government appears to have some sort of cease-fire with Mehsud. But 2008 may be the year that the government, now led by Bhutto's party, finally gets serious about the threat he poses. It is long overdue.

Bergen is author of The Osama bin Laden I Know