MADRID, Spain -- Jamal Ahmidan had been in and out of trouble for years in Spain and his native Morocco. He served time as a hashish and ecstasy dealer and gained a reputation for settling scores with a gun.

The 33-year-old rode a motorcycle and reportedly drank alcohol. He was a Muslim who didn't attend a militant mosque or sport the long beard favored by the strictly observant.

So when narcotics police bugged Mr. Ahmidan's phone in January and February 2004, they were sure the coded conversations were about a hashish deal. They weren't.

On March 11, 2004, authorities say, Mr. Ahmidan and three dozen accomplices planted bombs on four packed commuter trains in Madrid. They killed 191 people in one of the deadliest terror strikes since the Sept. 11, 2001, attacks on the United States.

They also destroyed the stereotype created by the Sept. 11 terror attacks of how Islamic radicals operate.

None of the Madrid bombers had ever been to Afghanistan or met anybody in Osama bin Laden's inner circle. A two-year investigation into the bombings has uncovered no evidence that al-Qaida helped plan, finance or carry out the bombings, or even knew about them beforehand.

Indeed, the Madrid bombings were a wake-up call. It is homegrown terrorists, not foreign al-Qaida operatives in sleeper cells like those who carried out the 9/11 attacks, who pose the greatest threat.

"We had their phones tapped and we weren't able to see it," a senior Spanish intelligence chief involved in the March 11 investigation told The Associated Press. "It was so preposterous to us that some drug dealers could be planning a terror attack that if we had been told the day before we would have ignored it."

The lesson has been learned, he said. "Today we are much more conscious [of the threat we face]."

To an unknowable degree, the Madrid attack and others reflect success in the hunt for the al-Qaida leadership responsible for killing nearly 3,000 people in New York, Washington and Pennsylvania five years ago.

A global dragnet against bin Laden's group has been far more effective than most people realize in neutralizing al-Qaida's top command. Osama bin Laden and his top deputy are still at large, but many of their most trusted men are not.

Abu Zubaydah. Ramzi Binalshibh. Khalid Sheikh Mohammed. Ahmed Khalfan Ghailani. Abu Farraj al-Libbi. All were once among al-Qaida's top commanders, and all were arrested in Pakistan and handed over to American custody, along with hundreds of lesser figures.

The one-time al-Qaida No. 3, Mohammed Atef, was killed in U.S. airstrikes in Afghanistan in 2001. Qaed Salim Sinan al-Harethi, al-Qaida's chief operative in Yemen, was blown up by a Hellfire missile in Yemen in 2002. More recently, al-Qaida in Iraq leader Abu Musab al-Zarqawi was taken out by two 500-pound bombs.

While others have stepped in to fill their shoes, many experts doubt the organization can replace the experience of its top leaders as quickly as they are lost.

Heinz Fromm, Germany's domestic intelligence chief, said earlier this year that bin Laden's group had been degraded into a "diffuse, amorphous organization." He added: "One today cannot talk any longer of a central leadership role of al-Qaida."

Magnus Ranstorp, a terrorism expert at Sweden's Center for Asymmetric Threat Studies, said the West has consistently misunderstood the nature of the enemy it faces, attributing to al-Qaida a level of control and leadership over local radical groups that it simply does not have.

"We in the West tend to look for structure where there is none. We talk about the terror CEO, or the al-Qaida franchise, and that is completely misleading in terms of the amorphousness of the adversary we're facing," he said. "In fact, there hasn't been any correlation or firm evidence that al-Qaida knew about or participated in any of the attacks since Sept. 11."

But Mr. Ranstorp and other counterterrorism experts caution that there is no cause for celebration. Progress against the core of al-Qaida has been overshadowed by a steady stream of deadly bombings by local groups, many of them Muslim extremists inspired to take up bin Laden's apocalyptic call.

In attack after attack, homegrown militants have shown they are capable of massive destruction, with or without al-Qaida's help.

Mr. Ranstorp, the Sweden-based terrorism analyst, said the fight against Islamic terrorism can boast a number of major successes, most notably against top al-Qaida leaders.

But he warned that the concept of worldwide jihad that bin Laden unleashed will not die easily, with local groups attaching local gripes to his global message.

"The spark has been lit," Mr. Ranstorp said. "In terms of the phenomenon of terrorism, we are fighting a losing battle, because it is beyond al-Qaida now."