US officials have distanced themselves somewhat from the Pakistani government’s swift — perhaps too swift — conclusion that Baitullah was behind the December 27 assassination of Benazir Bhutto. The slain former prime minister’s Pakistan Peoples Party also disputed that claim, pointing the finger instead at figures within the government.

Still, most US experts agree that Baitullah is the most likely culprit. Musharraf told a press conference last Friday that the tribal leader was behind most if not all of the 19 suicide bombings in Pakistan, including the two aimed at Bhutto, in the past three months. “He is the only one who had the capacity,” says one Afghan Taliban with close connections to Mehsud, Al Qaeda and Pakistani militants. (The source, who has proved reliable in the past, would speak only if his identity were protected.) Last week the Pakistani government produced an intercept in which it claims Baitullah was heard telling a militant cleric after Bhutto’s murder: “Fantastic job. Very brave boys, the ones who killed her.”

The Afghan Taliban source claims that Baitullah and his Qaeda allies had laid out remarkably intricate plans for killing Bhutto, who was a champion of secular democracy and a declared enemy of the jihadists. He says Baitullah and Al Qaeda’s Number 2, Ayman Al-Zawahiri — along with Zawahiri’s deputy, Mustafa Abu al-Yazid, Al Qaeda’s new commander of military operations in Afghanistan and Pakistan — had dispatched suicide bomber squads to five cities: Karachi, Peshawar, Lahore, Islamabad and Rawalpindi, where she was killed. Their orders were to follow Bhutto with the aim of assassinating her if an opportunity presented itself. (Two US counterterrorism officials, who asked for anonymity when discussing the investigation, say there are growing indications of Baitullah’s involvement in the assassination.) Baitullah and his allies have even grander plans, the Afghan source says. Her assassination is only part of Zawahiri’s long-nurtured plan to destabilise Pakistan and Musharraf’s regime, wage war in Afghanistan, and then destroy democracy in other Islamic countries such as Turkey and Indonesia.

Baitullah’s alleged emergence as the triggerman in this grand scheme illustrates the mutability of the jihadist enemy since 9/11. As recently as June 2004, Iraq was said to be Al Qaeda’s main battleground, and Abu Mussab al-Zarqawi was the terror chieftain whom US authorities worried about most. Baitullah was then a largely unknown subcommander in South Waziristan. But that same month, a US Hellfire missile fired from a Predator drone killed Nek Mohammad, the young, dashing and publicity-hungry tribal leader in Waziristan. Al Qaeda and tribal militants promoted the young Baitullah to a command position. His equally young Mehsud clansman, Abdullah Mehsud — a one-legged jihadist who had recently been released from two years of detention in Guantánamo — also seemed to be a rising star. But after the botched kidnapping of two Chinese engineers working on a dam in the tribal area, a local council backed by Al Qaeda removed Abdullah and replaced him with the little-known Baitullah, who was seen as being more levelheaded. (Abdullah was later killed in a shoot-out.)

Since then, Zarqawi has been killed by US forces, Iraq has receded as a haven for the Al Qaeda, and Baitullah has come into his own as a terrorist leader in newly unstable Pakistan. Last month a council of militant leaders from the tribal agencies and neighbouring areas named Baitullah the head of the newly formed Taliban Movement in Pakistan, a loose alliance of jihadist organisations in the tribal agencies.

One of Baitullah’s biggest successes came in August, when his men captured more than 250 Pakistani soldiers and paramilitary troops, who surrendered without firing a shot. Mehsud demanded the release of 30 jailed militants and the end of Pakistani military operations in the Mehsud tribal area as the price for the men’s release. To show he meant business, he ordered the beheading of three of his hostages. Once again, Musharraf gave in. On the day after Musharraf declared a state of emergency — which he claimed was aimed at giving him a stronger hand to fight militants like Baitullah — the Pakistani president released 25 jailed insurgents including several failed suicide bombers. Last week Mehsud’s forces captured four more Pakistani paramilitary troops in several brazen operations that may have led to the death of 25 of his men.

In his few statements to the press, Baitullah has made his agenda frighteningly clear. He vowed, in a January 2007 interview, to continue waging a jihad against “the infidel forces of American and Britain,” and to “continue our struggle until foreign troops are thrown out” of neighbouring Afghanistan. From his secure corner of Pakistan — a country run by a widely despised autocrat who, after Bhutto, has few real democratic successors — Baitullah may well wage that fight for a long time to come.

With Mark Hosenball in Washington