The investigation of the failed Times Square bombing has centered on a vital question: Did Pakistan-based terror groups train and direct the accused bomber?

Until now, Pakistan's Islamic insurgency has been viewed as essentially a home-grown movement, aimed at overthrowing the secular government and replacing it with an Islamic regime.

But clues pointing at involvement of the Pakistani Taliban, a close ally of al-Qaida, in the plot have new and troubling implications.

If the Pakistani Taliban played a role, the terror threat against the United States may be widening to include an organization with thousands of hardened fighters who have not previously struck in the West. Pakistan would likely come under even more American pressure to move aggressively against the fierce array of militant groups operating on its soil.

"It would be a big deal," said Charles S. Faddis, a former top counterterror official for the CIA. "It would be a new thing. The Pakistani Taliban is a sizable organization and with the Pakistani diaspora out there, they could tap into that. It's the whole idea of the threat evolving beyond al-Qaida."

The accused bomber, Faisal Shahzad, has admitted to training in the Waziristan region, a militant refuge where al-Qaida and the Pakistani Taliban are locked in a struggle with Pakistani ground forces and U.S. missile-firing drones. Shahzad, 30, told investigators that he had met with members of the Pakistani Taliban, according to a U.S. law enforcement official who spoke on condition of anonymity because the investigation remains open. Shahzad also indicated that he wanted to avenge recent slayings of militant leaders by U.S. missile strikes, the official said.

"He made references to having had some sort of contact with the Pakistani Taliban," the law enforcement official said. "He made reference to his motivation being revenge for U.S. activity and involvement in Pakistan."

The Pakistani Taliban want to impose an Islamic regime in Pakistan and help the Afghan Taliban and al-Qaida drive NATO forces out of neighboring Afghanistan.

Despite past claims and threats, the Taliban has shown little capacity to attack in the West. That's why experts remain cautious about attributing blame for the attack until investigators confirm the confession. There are also reports linking Shahzad to Jaish-e-Mohamed, a Pakistani extremist group that is an ally of al-Qaida and the Taliban and operates in Waziristan.

The tangled web of extremism makes pinpointing a culprit especially difficult, according to a U.S. intelligence official involved in the case.

"In Waziristan, it's hard to say an attack is purely one group or another," said the intelligence official, who also requested anonymity because the investigation is still open. "It's such a mixed bag."

The case apparently reinforces two trends, one scary and the other more comforting.

The scary trend: Islamic extremist networks are unleashing a contingent of U.S.-based operatives in a campaign to strike the United States. Shahzad's name joins a fast-growing list of alleged American extremists accused of terror plots from New York to Chicago to Dallas during the past year.

The comforting trend: Al-Qaida and its allies have a tendency to make mistakes. Commentators who assumed the crudely-assembled car bomb could not be the work of a bona fide, foreign-trained terrorist need to take a closer look at recent history.

During the past decade, militants connected to al-Qaida have repeatedly botched bombings, disregarded their own security guidelines and blundered into the hands of spies. Al-Qaida has not carried out a successful attack in the West since the London transport bombings that killed 52 people in 2005.

In recent years, toughened global enforcement and the missile strikes in Pakistan have depleted the fugitive leadership, targeted training compounds and diminished the flow of aspiring holy warriors from abroad. (The number of American trainees, however, appears to have increased.).

As a result, clumsy terror operations in the West are by no means an exception. In fact, mistakes have become almost a signature.

The errors in last week's Times Square plot -- from Shahzad's failing to ignite the car bomb to leaving his house keys in the ignition -- fit into that tradition. The composition of the propane-based bomb and the target resemble a bungled 2007 plot in which doctors of Middle Eastern descent attempted bombings in London and Glasgow.

The doctors radicalized largely on their own, but they had links to al-Qaida's affiliate in Iraq and an Iraqi doctor in the group may have trained in his homeland. After trying fruitlessly to detonate two car bombs in the heart of the London nightclub district, two suspects drove through the night to Glasgow and tried to ram another car bomb into the airport there. The Iraqi doctor died in that fiery failed attack, the only casualty.

There's no necessary contradiction between training camp experience and ineptitude in the field, between grooming by al-Qaida bosses and poor tradecraft, experts say.

In addition to the lack of sophistication of the Times Square bombing, the alliance between the Pakistani Taliban and al-Qaida adds to the ambiguity about affiliation of the potential masterminds. The Pakistani Taliban supply al-Qaida with sanctuary, a defensive ring and promising recruits.

Westerners including Bryant Neal Vinas, a Latino convert from Long Island, have made contact with the Pakistani Taliban before reaching al-Qaida. Weeks after arriving in Pakistan in late 2007, Vinas fought in a Taliban unit and gained the trust of his chiefs. He was then trained and cultivated by al-Qaida leaders, hatching a plot against the Long Island Railroad, according to U.S. and European court cases. Vinas was arrested in November 2008 and pleaded guilty to terror charges.

For years, Western intelligence officials have expressed doubt about the Pakistani Taliban's capacity to mount attacks outside its turf.

"If you really look at their track record, the reason people have dismissed their claims and threats is that they weren't perceived as having a capability to do this," Faddis said. "If they are now transforming, that's bad news."

The only previous Western plot that authorities attributed to the Pakistani Taliban turned out to involve al-Qaida as well. In January 2008, Spain's para-military Guardia Civil arrested 11 Pakistanis in Barcelona after a tip from a French informant who had infiltrated the group and traveled with them to Spain from northwest Pakistan.

Prosecutors charged the men with plotting an imminent bombing on the Barcelona subway. Initial testimony indicated that the plotters acted under the orders of Baitullah Mehsud, who led the Pakistani Taliban at the time and later claimed responsibility.

During the investigation and trial, however, it was revealed that al-Qaida had played a role in the operation, according to Spanish and U.S. anti-terror officials. The defendants were convicted.

"It was a joint venture by the Taliban and al-Qaida," a U.S. anti-terror official said. "And the New York case looks like it could be the same kind of thing."

Suspicions that the Pakistani Taliban is involved in the Times Square plot have been reinforced by Shahzad's confession and recent statements from the group's leadership threatening attacks on the United States.

In the militant strongholds of Waziristan, the U.S. and its allies face an increasingly intertwined swarm of terror networks. In addition to the Pakistani Taliban, the region hosts the Arab-dominated forces of al-Qaida, which are thought to number in the hundreds.

Also present are the Central Asians and Turks of the Islamic Jihad Union and the Pakistani networks Jaish-e-Mohamed and Lashkar-e-Toiba. The latter groups have concentrated on the conflict with India for Kashmir and have longtime ties to Pakistani security forces. Official protection has helped the two groups survive periodic announced crackdowns, Western counterterror officials say.

The assorted networks are allies, assist each other and espouse al-Qaida's agenda of global jihad, though tensions and rivalries flare and their training facilities are usually separate.

Training and plotting are necessarily makeshift and rushed. Recent European and U.S. investigations revealed that al-Qaida recruits moved frequently among safe houses and compounds. Instructors conducted training in weapons, explosives and tradecraft in cramped courtyards with small groups of trainees.

Nonetheless, al-Qaida has managed to launch repeated plots against the West. Despite the array of militant groups operating in Pakistan, most of those plots have been traced back to a cadre of veteran planners and trainers in al-Qaida's external operations unit. It is a small world: a single figure -- a Briton of Pakistani descent named Rashid Rauf -- served as a handler and communications specialist directing Western operatives for at least four years, investigators say

Rauf has been linked to the London transport attacks of July 7, 2005, a foiled plot to blow up U.S.-bound airliners from Britain in 2006, Vinas' embryonic plot on the Long Island Railroad, and last year's aborted plot by an Afghan-American to bomb the New York subways. A missile strike killed Rauf shortly after Vinas was captured in late 2008.

The U.S. missile onslaught has killed a roster of veteran leaders and spread fear of spies. The Pakistani army's recent offensive has further cranked up pressure. The reduced time of training and declining quality of trainers and recruits alike has hurt al-Qaida's effectiveness, experts say.

"In the days before Sept. 11, recruits would train for as much as nine months and become real experts in explosives and bomb-making," said Louis Caprioli, the former counterterror chief for France's DST intelligence service. "Now the training lasts weeks or a few months at most. That's probably the reason the bomb in Times Square was rudimentary. It was easier and safer to build. It takes more preparation, in fact knowledge of chemistry, to prepare explosives like TATP, which is very volatile and can blow up on you."

It's not yet clear how long Shahzad trained and how much direction he had. In the often opportunistic world of Islamic terrorism, it's quite possible he underwent limited instruction and was given freedom to develop his own mission, experts said.

Even well-trained al-Qaida terrorists, who are often depicted as cold, skilled and unstoppable, have shown a notable propensity for error. Briton Richard Reid underwent extensive courses in Osama bin Laden's Afghan camps and conducted reconnaissance missions in Israel before bungling his attempt to blow up a Miami-bound jet in December 2001 when he was baptized forever as the "shoe bomber."

On July 21, 2005, an Eritrean-born Briton who had been trained by al-Qaida in Pakistan prepared four backpack bombs for a follow-up to the strike on the London transport system two weeks earlier, but the explosives did not detonate and the attackers were arrested. Last year, the Nigerian "Christmas bomber" failed to carry out an attack in the sky over Detroit that was very similar to Reid's.

Even successes have been marked by lapses. Although the Madrid train-bombings of 2004 killed 190 people and affected the outcome of a national election, the bombers were surprisingly sloppy. Their leader narrowly avoided discovery when police pulled him over for speeding. He mouthed off to the police even though he had a fake ID and a trunk full of dynamite. His group was under surveillance by three separate Spanish security forces.

In a case in the Netherlands in 2004, a group of wild young extremists involved in the assassination of a filmmaker had been so thoroughly infiltrated that the Dutch intelligence service was able to wire their apartment for sound. Police did not detect the plot by a solo gunman to kill the filmmaker, but raided the apartment after hearing the youths plan follow-up attacks on politicians.

"Rare are the ones who really know what they are doing, the [9/11 mastermind] Mohamed Attas and Mohamed Sidique Khans," the ringleader of the London bombers, the U.S. intelligence official said. "It's much more common to see the bumblers like Richard Reid."

Shahzad may have lacked expertise, but that does not mean he wasn't dangerous, authorities say. Although investigators have not identified any U.S.-based accomplices in the Time Square plot, they are hunting for possible like-minded associates who could pose a threat. Previous cases show that radicalization usually happens in a group setting.

"We want to make sure he wasn't part of a cluster," the intelligence official said. "Are there still three or four of his buddies out there? Remember that the Madrid attacks were done by people who had been on the margins of a cell that was broken up in 2001."

Unlike many terror suspects in the West, Shahzad does not appear to have come to the attention of anti-terror agencies before the attempted attack. His profile embodies the fears of investigators and the hopes of terrorists, according to Faddis, the former CIA counterterror chief.

"That's what they want: a U.S. citizen with a life and family here," he said. "A 'clean-skin,' someone who isn't known as an extremist. These guys are valuable and they are actively sought out."