AMMAN, Jordan — The telephone rang at 7 a.m. on New Year’s Eve, and then the heavily accented voice of a stranger — possibly an Afghan — told the man who answered what had happened to one of his sons who disappeared a year ago.

“They said that Humam had made a big operation against the C.I.A.,” said a brother of Humam Khalil Abu Mulal al-Balawi, the 32-year-old Jordanian of Palestinian heritage who killed seven Americans at a remote outpost in Afghanistan last week.

“He is a hero,” the caller said, according to the brother.

It was only later that day, when the family learned more details about the deaths of the Central Intelligence Agency operatives, that the bomber’s family became certain that Mr. Balawi, a doctor, was not, as they thought, tending to sick and injured Palestinians in Gaza but was at the center of a complex espionage operation that backfired to deadly effect.

Western government officials say Mr. Balawi was recruited by Jordanian intelligence agents and taken to Afghanistan to infiltrate Al Qaeda by posing as a foreign jihadi. There he attended a meeting with the C.I.A. and blew himself up, killing seven Americans and his Jordanian supervisor, a distant cousin of King Abdullah II.

Details about Mr. Balawi and the operation are slowly emerging, with a Jordanian official here saying that Mr. Balawi had traveled to Pakistan and from there began volunteering information by e-mail “on Al Qaeda and its planned operations in Jordan and other nations.”

“He was engaged in an empathetic and friendly way,” the official added, “with a view to trying to verify the information.”

The official declined to identify the value of Mr. Balawi’s communications, saying only that “he provided information that warranted attention, that we thought was worthy of looking into.” The Jordanian intelligence services shared that information with other countries, he said, including the United States.

Mr. Balawi’s father, Khalil, said Wednesday night that he was still confused by conflicting reports about exactly what had happened to his son.

“We don’t have any information,” he said, as he returned from the mosque near his ground-floor apartment on Urwah bin al-Ward Street in the Nuzha district here in Jordan’s capital. “Everything we hear is contradictory.”

So close a watch is being kept on the house that Mr. Balawi’s youngest brother has been arrested, according to the family, and the brother who answered the door at the family home declined to give his first name, saying only that he was an engineer who had flown back from Dubai to look after his parents. He said that he feared “consequences” if he spoke in public and that the family had been repeatedly warned not to speak to the media.

He described Mr. Balawi as a “very good brother” and a “brilliant doctor,” saying that the family knew nothing of Mr. Balawi’s writings under a pseudonym on jihadi Web sites. He said, however, that his brother had been “changed” by last year’s three-week-long Israeli offensive in Gaza, which killed about 1,300 Palestinians.

The brother said that Mr. Balawi was arrested by the Jordanian authorities after volunteering with medical organizations to treat wounded Palestinians in Gaza. The family is itself of Palestinian origin, from a tribe in the Beersheba region.

He voiced no criticism of his brother’s actions, instead blaming unnamed people who he felt had pushed him to act. He said Mr. Balawi had felt under “huge pressure” after his arrest, had immediately “disposed” of his computer, stopped using e-mail and disappeared altogether shortly afterward. “If you catch a cat and put it in a corner, she will jump on you,” the brother said.

Posts on jihadi Web sites have hailed the bombing as a triumph and have praised its perpetrator, some using Mr. Balawi’s online persona, Abu Dujana al-Khorasani.

On Tuesday, a message on the Web site muslm.net by a member called “The Optimist” said: “If it is true that the person who carried out the operation is the writer Abu Dujana al-Khorasani then I swear to God it is a genuine operation coming from this hero. It is enough that it eradicated some important elements of the C.I.A. Even the American officials are shouting in the media because of this hard blow.”

The bomber’s mother, Shanara Fadel al-Balawi, told Agence France-Presse that her son “was never an extremist.” She said that her son was “conscientious” and “a good student at a Jordanian public school” who had applied last year for a visa to study in the United States.

The Jordanian official confirmed that Mr. Balawi was questioned by intelligence officials a year ago after writing on jihadi Web sites but said that he was released because there was not enough evidence to try him.

Soon after, Mr. Balawi left for Pakistan, ostensibly to pursue his medical career, said the official, who declined to be identified while the American investigation was under way. Some months later, he said, Mr. Balawi “contacted us by e-mail.”

“In cooperation with the Americans we tried to lure him to verify the information that he provided, to check it out,” said the official. He declined to be drawn out on operational details like who exactly was dealing directly with Mr. Balawi. But he did say: “We aren’t in Afghanistan. The Americans are in Afghanistan, and Pakistan.”

He also insisted that the bombing had not strained Jordan’s ties with the United States, and that Jordan would continue its “solid, very effective and very fruitful” cooperation with the Americans.

Citing Al Qaeda’s attacks on Jordan, including three bomb blasts in 2005 that killed more than 50 people at hotels in Amman, he said that Al Qaeda was Jordan’s enemy as much as it was America’s.

“These guys killed our own,” he said. “They are our enemy. The United States is a partner, it is an ally, we have a joint enemy and we are going to stand up against it together.”