An Egyptian biochemist who was arrested here for questioning about the London terror bombings grew up in a gritty neighborhood on Cairo's outskirts but built a successful academic career in the United States and Britain, neighbors and former colleagues said Friday.

The Interior Ministry here identified the man as Magdy Mahmoud Mustafa Nashar, 33, a researcher at Leeds University in Britain. It said he was on a six-week vacation in Cairo, where his family lives, and had planned to return to Britain afterward.

British media have reported that Nashar served as a go-between in renting a townhouse that was raided by police Tuesday in Leeds, a diverse industrial city north of London where three of the four suspected bombers lived. British law enforcement officials said they found explosives in the house.

Nashar's arrest broadened the investigation into the attacks, the worst instance of terrorism on British soil. In view of his travels -- academic training took him from Cairo to North Carolina to England -- his whereabouts and contacts quickly interested U.S. and British investigators, as well as those in Egypt, who remain wary of the specter of Islamic militancy.

He denied to interrogators that he played any role in planning the July 7 attacks, which killed at least 54 people, including four bombers. "He pointed out that all of his belongings were still in his apartment" in Britain, the ministry statement said.

Egyptian officials said little else about the arrest or whether Nashar was considered a witness or suspect. In London, police chief Ian Blair said Britain might dispatch officers to Cairo and would consider extradition if necessary.

Word of Nashar's detention prompted surprise among some colleagues at Leeds University and Egyptians who grew up with Nashar along a leafy but poor and crowded street near the wealthy Cairo suburb of Maadi.

"For me he was fine, nothing abnormal in any way," said John Findlay, a Leeds professor of biochemistry. "The whole thing's a shock. You don't think about anything like this with colleagues. We know almost nothing about their background. The university is made up of all sorts of people, you don't presume anything."

In his former Cairo neighborhood, he was remembered as a somewhat quiet, polite youth, who had lived with his parents and a younger brother and sister on a modest, second-floor apartment in a narrow street prone to ruptures of sewage.

"He wasn't involved in anything political," said Mustafa Mahmoud, 41, a day laborer. "Look at the area. We all live next to each other, we all know everything about each other, and I know there wasn't anything political about him."

Residents said Nashar's family left the neighborhood two years ago. They said the father, a blacksmith, still visits his shop on the building's first floor once or twice a week, but no one had seen the younger Nashar in years. The apartment is shuttered, with a worn, red-and-orange sheet hanging over the balcony and a rusted iron grill.

His neighbors described a typical upbringing in a neighborhood of low-slung buildings known as shaabi, the kind of lower-class stretch of brick and concrete that dominates this city of 15 million.

His younger brother Mohammed played an organ at wedding parties, and Nashar himself was fond of the oud, an Arabic stringed instrument, they said. Like most people in the neighborhood, he prayed regularly but was not preternaturally religious, they said. As a youth, he would often join soccer games after attending dawn prayers at the nearby Nasr Mosque, a modest, one-story stone building.

Many people here saw Nashar as a rare success for the neighborhood. He earned a degree from Cairo University, went on to graduate studies at North Carolina State University in 2000, finally earning a doctorate from Leeds in May. His research was sponsored by the prestigious National Research Center in Cairo, where the Interior Ministry said he worked as a researcher.

Mohammed Ali, 27, a barber in the neighborhood, said he didn't believe Nashar was involved in the attacks. "Someone who studied in America, who made something of himself, would do something like this?" He shook his head. "I don't think so."

Perhaps , Ali said, he left Britain because "he was scared of what would happen to Muslims and Arabs in London. Maybe that was an issue. Or maybe he came home on a typical vacation to see his parents and his family."

Ahmed Hanafi, a neighbor who described himself as a friend of Nashar's, said he last saw his father three weeks ago. "I asked him about Magdy, and he told me, 'He's fine, he's married, and he's in England.' "

In a telephone interview, Nashar's brother, Mohammed, told the Arab satellite network al-Jazeera that Nashar had returned to Cairo on June 30, "before anything happened." He denied that his brother was the kind of man who would plan the attacks in London.

At Leeds University, colleagues said his books still appeared to be in his office and that he seemed set to return. "Everyone thinks he's innocent. There's no way he was involved in all this. He's not part of their group. He's an Arab," said a student in the Medicinal Chemistry Department who knew Nashar but asked not to be named.

"People are saying he fled to Cairo. He's a student who finished his PhD. Everyone goes home around this time."

Special correspondents Ben Schofield and Shiv Malik in Leeds contributed to this report.

Om Nabil, an Egyptian, talks about Nashar's family in front of their Cairo home; Nashar was a rare local success.