This article is based on reporting by Neil MacFarquhar, Jim Yardley and Paul Zielbauer and was written by Mr. Yardley.

recisely two years ago, not long before he traveled to the United States to coordinate the worst terrorist attacks in history, Mohamed Atta attended a wedding. The event was held in the German port city of Hamburg, where Mr. Atta had recently earned a university degree, but this was not the marriage of a college friend.

The groom was Said Bahaji, now the focus of an international manhunt for his suspected role in the Sept. 11 attacks. Prominent among the guests was Mamoun Darkazanli, a Syrian businessman suspected of being a financial conduit for Osama bin Laden's Al Qaeda organization. Another guest was Mr. Atta's friend, Marwan al-Shehhi, whom authorities say crashed the second hijacked airliner into the World Trade Center.

This was not what Mr. Atta's father in Egypt had imagined when he sent his son abroad to earn the sort of academic degree that would bring him prestige and success at home. Instead of becoming an architect or an urban planner, Mr. Atta had become an Islamic terrorist.

Mr. Atta's path to Sept. 11, pieced together from interviews with people who knew him across 33 years and three continents, was a quiet and methodical evolution of resentment that somehow ?and that how remains the essential imponderable ?took a leap to mass-murderous fury.

Mohamed Atta, the suspected mastermind of the Sept. 11 terror attacks, with his sister on vacation in the 1980's. A shy child, he became an efficient mass murderer.   Interactive: Hijacking Suspects News Analysis: In Germany, Terrorists Made Use of a Passion: An Open Democracy (October 5, 2001) Disavowal: Father Denies 'Gentle Son' Could Hijack Any Jetliner (September 19, 2001)

The youngest child of a pampering mother and an ambitious father, Mr. Atta was a polite, shy boy who came of age in an Egypt torn between growing Western influence and the religious fundamentalism that gathered force in reaction. But it was not until he was on his own, in the West, that his religious faith deepened and his resentments hardened. The focus of his disappointment became the Egyptian government; the target of his blame became the West, and especially America.

In Hamburg, his life divided into before and after. He would disappear more than once, and officials say they have strong evidence that he trained at Mr. bin Laden's terrorist camps in Afghanistan during the late 1990's. It was also in those years, German investigators say, that Mr. Atta became part of the Hamburg cell that became a key planning point for the Sept. 11 attacks.

"I remember that he changed somewhat," said Dittmar Machule, his academic supervisor at Hamburg Technical University. "He looked more serious, and he didn't smile as much."

His acquaintances from that time still cannot reconcile him as a killer, but in hindsight the raw ingredients of his personality suggest some clues. He was meticulous, disciplined and highly intelligent.

His vision of Islam embraced resolute precepts of fate and destiny and purity, and, ultimately, tolerated no compromise. He ate no pork and scraped the frosting off cakes, in case it contained lard. He threatened to leave the university unless he was given a room for a prayer group. He spoke of a desire to marry, but was remote to the point of rudeness with women, considering most insufficiently devout.

Those who had known him as a quiet student say his demeanor became more brooding, more troubled. The most obvious change was both cosmetic and spiritual: he had grown the beard of an Islamic fundamentalist.

A Shy and Sheltered Boy

The genteel gloss of the Abdein neighborhood of Cairo had dulled to shabby disrepair by the early 1980's when Mohamed al-Amir Atta entered his teenage years. The government workers who had once lived well on $100 a month found themselves in a vortex of downward mobility, working second and third jobs to survive.

Mr. Atta's father, a lawyer, considered his neighbors inferior, even if he, too, feared the economic undertow. Neighbors recalled an arrogant man who often passed without a word or a glance.

The family was viewed as thoroughly modern, the two daughters headed for careers as a professor and a doctor. The father was the disciplinarian, grumbling that his wife spoiled their bright, if timid, son, who continued to sit on her lap until enrolling at Cairo University.

"I used to tell her that she is raising him as a girl, and that I have three girls, but she never stopped pampering him," Mohamed al-Amir Atta Sr. recalled in a recent interview at his apartment.

In a high school classroom of 26 students grouped by their shared given name, Mohammed Hassan Attiya recalled that Mr. Atta focused solely on becoming an engineer ?and following his father's bidding.

"I never saw him playing," Mr. Attiya said. "We did not like him very much, and I think he wanted to play with the rest of the boys, but his family, and I think his father, wanted him to always perform in school in an excellent way."

The social, political and religious pressures roiling Egypt exploded in 1981 with the assassination of President Anwar el- Sadat, the first Arab leader to make peace with Israel. Fundamentalists decried him as a puppet of the West, a traitor to Islam.

Even for a boy as sheltered as Mr. Atta, the disillusionment on the streets would have been difficult to ignore. His father, without explanation, says his son began to pray in earnest at 12 or 13, an awakening that coincided closely with Sadat's slaying. But the elder Mr. Atta said his son's religious inclination did not extend to politics.

"I advised him, like my father advised me, that politics equals hypocrisy," his father said.

The boy refused to join a basketball league because it was organized by the Muslim Brotherhood, Egypt's most established religious political organization, which also recruited from Cairo University's engineering department but not, apparently, Mr. Atta, who graduated from there in 1990.

His degree meant little in a country where thousands of college graduates were unable to find good jobs. Though Mr. Atta found work with a German company in Cairo and was reluctant to leave his mother and sisters, his father convinced him that only an advanced degree from abroad would allow him to prosper in Egypt. Soon he was headed to Hamburg Technical University on scholarship.

"I told him I needed to hear the word `doctor' in front of his name," his father recalled. "We told him your sisters are doctors and their husbands are doctors and you are the man of the family."

From initial appearances, the slender young Mr. Atta remained the same person in Hamburg that he had been in Egypt ?polite, distant and neatly dressed. He answered a classified ad and was hired part- time at an urban planning firm, plankontor. He impressed his co-workers with his diligence and the careful elegance of his drafting.

Yet he must have felt unmoored, on his own in a strange land. He took refuge in the substantial population of Turkish, African and Arab immigrants living in the blue- collar Harburg section surrounding the university. There, his religious faith, still tentative in Egypt, took deeper hold.

He brought a prayer carpet to his job and carefully adhered to Islamic dietary restrictions, shunning alcohol and checking the ingredients of everything, even medicine. He had his choice of three mosques, but the two closest to campus were dominated by Turks, whom many local Arabs disdained as less devout and too sympathetic to America.

Instead, Mr. Atta often prayed at the Arabic-language Al-Tauhid mosque, a bleak back room of a small shop where the imam, Ahmed Emam, preached that America was an enemy of Islam and a country "unloved in our world."

Mr. Atta's academic focus was Arab cities, specifically preserving them in the face of Western-style development. He returned to Cairo for three months in 1995 to observe a renovation project around the old city gates, Bab Al-Nasr and Bab Al-Futuh. The project, he came to believe, involved little more than knocking down a poor neighborhood to improve the views for tourists.

"It made him angry," recalled Ralph Bodenstein, one of two German students in the program. "He said it was a completely absurd way to develop the city, to make a Disneyworld out of it."

Over meals with Mr. Bodenstein and the other German student, Volker Hauth, Mr. Atta spoke bitterly about the government's suppression of Islamic fundamentalist groups and the clinics and day care centers they had built in ignored neighborhoods.

His sympathy for their cause, Mr. Atta feared, would doom his own future at home. His only hope for a good urban-planning job in Egypt was to be hired by an international organization. He tried but never was. The young man sent West to better his future at home now worried that he had no future in Egypt at all.

He returned to Hamburg in 1996, and investigators say he eventually moved into an apartment at 54 Marienstrasse with two other suspected hijackers, Mr. al-Shehhi and Ziad Jarrah.

In November 1997 he paid an unexpected visit to his academic supervisor, Professor Machule, to discuss his thesis, then disappeared again for about a year. Federal officials say they have strong evidence that he trained at an Al Qaeda camp in Afghanistan during the late 1990's, which could explain his whereabouts in 1998.

He reappeared in Hamburg in early 1999, the period that German investigators connect him with the cell of about 20 other suspected terrorists. At the university, he insisted on a room for an Islamic prayer group. A student council representative demurred, suspicious that such organizations were cover for terrorist recruitment.

"He said, `This is about my life. If I cannot pray here, I cannot study here, at this university,' " said the council representative, Marcus Meyer.

Mr. Atta's degree had been on hold; suddenly, finishing it became imperative. He submitted his thesis in August 1999. When he successfully defended his thesis, graduating with high honors, Mr. Atta refused to shake hands with one of the two judges, a woman.

His father has told reporters that his son earned a masters degree in Germany, but in fact, Mr. Atta received only an undergraduate degree. But his attentions were already elsewhere. He began preparing to go to America.

A Disciplined Perfectionist

With few exceptions, Mohamed Atta regarded the Americans who crossed his path with the same contempt his father once reserved for his Cairo neighbors. He was polite when he had to be ?to rent a car or an airplane ?but the mildness recalled by his friends in Egypt and Germany was gone, as was his beard.

He arrived in June at Newark International Airport and would spend the next 15 months in near perpetual motion, earning a pilot's license in Florida during the last six months of 2000, then spending the first nine months of 2001 traveling across the country and at least twice to Europe.

The awful efficiency of the attack demanded a leader with a precise and disciplined temperament, and Mr. Atta apparently filled that role. Federal investigators have told a House committee that in the fall of 2000, as he was in the middle of flight training in Venice, Fla., Mr. Atta received a wire transfer of more than $100,000 from a source in the United Arab Emirates. Investigators believe the source was Mustafa Ahmad, thought to be an alias for Shaykh Said, a finance chief for Mr. bin Laden.

For much of 2001, Mr. Atta appeared to make important contacts with other hijackers or conspirators. He traveled twice to Spain, in January and July, and officials are investigating whether he met with Al Qaeda contacts. He also used Florida as a base to move around the United States, including trips to Atlanta, where he rented a plane, to New Jersey, where he may have met with other hijackers, and at least two trips to Las Vegas. Everywhere he went, he made hundreds of cell phone calls and made a point to rent computers for e-mails, including at a Las Vegas computer store, Cyberzone, where customers can play a video game about terrorists with a voice that declares "terrorists win."

While Mr. Atta was considered a perfectionist, he was not infallible. Brad Warrick, owner of a rental agency in South Florida where Mr. Atta returned a car two days before the attack, found an ATM receipt and a white Post-it note that became key evidence. Mr. Atta's decision to wire $4,000 overseas shortly before the attacks left an electronic trail that investigators believe is leading back to Al Qaeda. Finally, authorities found his luggage at Logan Airport in Boston, containing, among other things, his will. It remains unclear if the bag simply missed the connection to his flight.

Or perhaps the introvert, the meticulous planner, the man who believed he was doing God's will, wanted to make certain the world knew his name.