When the attacks on the World Trade Centre and the Pentagon succeeded so horribly in 2001, billions of decent people around the world were taken off guard.

Who would slaughter so many innocents, including children? Who was al-Qaida? Who was this Osama bin Laden? Why? How?

Perhaps the saddest aspect of all these questions is that the answers had been known to security operatives, bureaucrats and politicians long before 9/11.

Enough frightening information about these virulent jihadists had been gleaned before that September to prevent the catastrophe.

Because so little of that information was shared or acted upon, the massacres were allowed to happen.

After the event, conspiracy theorists proliferated as ultraconservative Republicans gobbled up the American economy and increasingly dominated foreign and domestic policy in the name of national security.

But they were simply opportunists. The only conspiracy was bin Laden’s.

If Lawrence Wright’s new account of the events and personalities behind 9/11, The Looming Tower, were a movie script, it would be deemed ridiculously improbable, a B-flick farce, owing to the myriad missed cues and missed opportunities.

In fact, the failure of communication between government branches charged with US security even acquired its own theme song, Wright reveals.

“The agents on the I-49 were so used to being denied access to intelligence that they bought a CD of a Pink Floyd song, Another Brick in the Wall. Whenever they received the same formulation about ‘sensitive sources and methods,’ they would hold up the phone to the CD player and push Play.”

Wright’s meticulously researched history begins with the first theorists of contemporary jihad, then traces their lives, their motivations and confluences.

He then introduces us to American operatives who fought against the bureaucratic timidity of their own superiors to prevent the 9/11-type event they feared was at hand.

The best, brightest and bravest were treated like Chicken Littles.

The author, who has in fact written a novel, God’s Favourite, along with screenplays, a play and five nonfiction books, recreates their obsessions and foibles with the care of a master novelist; in his hands, the evil, the brave, the prescient and the inept achieve some just desserts.

One of the essential components of misunderstanding al-Qaida and terrorism in general, is the tendency to dismiss the perpetrators as ‘monsters’ and settle for that.

In fact, the evil carnage wrought on September 11 in New York and elsewhere at many other times was perpetrated by human beings — a far more unsettling fact.

Wright cuts right to the chase with this approach.

The man who set the philosophical foundations for the mayhem that was to follow was the Egyptian educator and writer Sayyid Qutb.

He began a process of rationalizing violent actions that would prove abhorrent to true Muslims.

Shortly after the Second World War, seeking more education and to escape from possible prosecution as a troublemaker at home, Qutb sailed for America.

En route, the young bachelor heard a knock at his stateroom door. He opened it to find a half-naked young woman who offered to share his bed with him.

Appalled, he slammed the door in her face. “I instantly thanked God for defeating my temptation and allowing me to stick to my morals,” he later recalled.

Rabble rouser Qutb, who would write, “I hate those Westerners and despise them!” because of US support for Israel, was hanged in Egypt in 1966, thus becoming a martyr and a rallying point for future Islamic revolutionaries.

As bin Laden’s old university friend and co-conspirator Mohammed Jamal Khalifa would later admit: “We were trying to understand what Islam has to say about how we eat, who we marry, how we talk. We read Sayyid Qutb. He was the one who most affected our generation.”

The yearning for sex and the abhorrence of female sexuality became a dominant feature of extremist Islam.

Young men, frustrated by exhortations against sex, would be encouraged to become holy war martyrs and promised 73 virgins in paradise.

Ayman al-Zawahiri, the son of a physician, grew up in relatively privileged circumstances in Egypt to become a physician himself.

Zawahiri was a brilliant student — by some accounts, a genius — but early on he began to display a rebellious streak that would widen into zealotry:

“The vice-president of Egypt, Hussein al-Shaffei, stopped his car to offer the boys a ride. Shaffei had been one of the judges in the roundup of Islamist in 1954 … Ayman said, ‘We don’t want to get this ride from a man who participated in the courts that killed Muslims.’”

Also among those who take on a very human dimension through Wright’s prose is Osama bin Laden himself.

He was the son of a self-made billionaire, a one-eyed Yemeni labourer who went on to found a construction empire that would eventually be strong enough to prop up Saudi Arabia after profligate princes squandered the treasury.

After 9/11, bin Laden would refer to the benefits of his experience in construction.

“Due to the nature of my profession and work, I figured that the fuel in the plane would raise the temperature of the steel until it becomes red and almost loses its properties.”

Far from becoming a construction magnate, bin Laden wound up an impoverished fugitive, a fact that caused him serious, ultimately destructive, marital stresses with several of his wives.

Of course, those charged with protecting the US from such fanatics were all-too-human as well.

None more so than John O’Neill, the FBI agent who struggled for so long to wake America up to the fact that a great evil was brewing in the Middle East.

O’Neill retired from the force in some disgrace, in part for having been impolitic in trying to wake up his superiors to the threat, and in part because his personal life was a miasma of adulterous relationships and wild spending.

Another agent, who did O’Neill’s taxes, realized how vulnerable poverty would make O’Neill to selling out.

“Gee, John,” he said, “you’d be a candidate for recruitment.”

O’Neill, eventually took on a high-paying job as head of security for the World Trade Centre and died at his post on 9/11.

Would his warnings have been listened to if he’d been less profligate? Chances are his recklessness, so visible in his private life, also made it possible for him to think, speak and act outside the box in his professional life.

As the destruction of the towers approaches in Wright’s narrative, the drama of prescient agents labouring to piece together the impending scenario becomes more infuriating as it becomes more urgent.

Next to O’Neill, no FBI agent struggled against intransigence more than Ali Soufan.

Soufan travelled to Yemen seeking details about the terrorist bombing of the USS Cole.

A whole series of connections would have come together in Soufan’s mind if he had been better supported by the rest of America’s security apparatus:

“If the CIA had responded to Soufan by supplying him with the intelligence he requested, the FBI would have learned of the Malaysia meeting and of the connection to Mihdhar and Hazami. The bureau would have learned — as the agency already knew — that the al-Qaida operatives were in America and had been for more than a year.”

The significance of this registered with Soufan in a big way following 9/11.

“When Soufan realized that the agency and some people in the bureau had known for more than a year and a half that two of the hijackers were in the country, he ran into the bathroom and retched.”

There’s much minute detail in this book and readers might wonder if all of this distressing information is well documented.

The narrative ends on page 373, the book on page 470, and most of those 67 pages are devoted to bibliography, acknowledgements and notes.

Details of the conspiracy were found in al-Qaida computers and phone records.

Some radicals co-operated with agents after realizing how many innocent people, including Muslims, died in the towers.

And journalists dug as bureaucrats and politicians made their excuses.

The amount of collating that was demanded by this effort is staggering. The literary skill with which Wright brings evil and incompetence, courage and vulnerability together on the terrible day in September demands a wide and humble readership.

The Looming Tower: al-Qaida and the road to 9/11, by Lawrence Wright, Knopf, 470 pages, $36.95 hard cover