ISLAMABAD, Pakistan — On leafy Hillside Road, tucked against the Margalla Hills, commandos behind sandbag bunkers guard the villa of a scientist who's exalted in his homeland as the "father of the bomb" but scorned abroad as a "nuclear jihadist."
Automatic weapons at the ready, the guards study every vehicle that passes the ivy-covered estate of Abdul Qadeer Khan, who ushered Pakistan into the nuclear age and ran a virtual bazaar of nuclear technology and know-how for "rogue" nations such as Iran, Libya and North Korea.
For the past four years, Khan has been under house arrest for confessing to selling nuclear-weapons secrets. Some Pakistanis, who revere Khan as a hero, say it's time to let him go free and recover from his recent prostate cancer in peace.
Khan still holds the solutions to many riddles of an increasingly alarming global nuclear age. Some of his knowledge could embarrass Pakistanis in power, but also could shed light on the extent of nuclear programs and weapons dealers in the world's dark alleys.
Some things about Khan's life also remain mysteries.
Whom are the sentinels outside his villa guarding against? Are they protecting Khan from foreigners who might abduct him to jump-start their own nuclear programs? Do some former colleagues want to do him in? Or are the guards there to keep a lid on Khan, who reportedly boils at allegations that greed — not loftier goals — drove him to sell nuclear secrets, and now may want to spill the beans?
What's certain is that A.Q. Khan knows much more than he's said about how he, an ambitious metallurgist living in Holland, managed to connive and steal enough secrets to build a flourishing nuclear program in Pakistan, turning his state laboratory into a virtual nuclear Wal-Mart or "Nukes 'R' Us."
"I don't think the whole story has been told, even with a dozen books about him," said Shahid ur-Rehman, a local journalist and author who said he'd interviewed Khan 20 to 25 times for a not-yet-published account.
Despite rampant charges over the years that Islamabad has sold its nuclear know-how, Pakistan stonewalls all foreign requests to speak with Khan. It asserts that its own interrogators questioned Khan over a two-year period, that he acted as a ringleader of a group with no broad links to the state and that all pertinent information was released.
"It is a dead horse that has been beaten, flogged, many times over," said retired Lt. Gen. Khalid Kidwai, the chief of Pakistan's nuclear-weapons program.
Disbelieving U.S. and European lawmakers have pressed Pakistani President Pervez Musharraf to permit investigators from the International Atomic Energy Agency to interrogate Khan. The Bush administration, which considers Musharraf a key ally in the war on terrorism, largely has avoided the issue.
"We have basically accepted President Musharraf's argument that we cannot have access to A.Q. Khan because it would further destabilize his government," said Jon Wolfsthal, a nuclear expert at the Center for Strategic and International Studies, a center-right policy institute in Washington. "The political decision has been made that we need Musharraf . . . more than we need to get access to Khan."
That frustrates some experts, who say that Pakistan has whitewashed the Khan case to hide its continued involvement in black-market procurement and sale of nuclear materials. Pakistan also blocks potential leads into whether nations such as Syria have nuclear programs and whether North Korea sought to enrich uranium as well as make bombs from plutonium.
"I don't think anyone feels confident the A.Q. Khan network was put to sleep. We can't trust the Pakistanis to be forthcoming on this issue because they haven't been," said Christine Fair, a South Asia analyst at the RAND Corp. research center.
Fair said that Khan's secrets, if revealed, would shed light on the companies and brokers who helped Pakistan's military supply and maintain its nuclear arsenal to this day.
"He's got 30 years-plus not as a rogue actor but as a state actor. So they are not going to let anyone talk to him," Fair said, adding that Pakistan's military chiefs don't want Khan revealing "everyone who's in the nasty network."
Khan rose from humble origins. His Muslim family fled from Bhopal, India, to Pakistan after British India was partitioned in 1947. In the early 1960s, Khan made his way to Europe, where he studied metallurgy, eventually obtaining a job with a subcontractor to a uranium-enrichment facility that provided fuel for European nuclear reactors.
He married a South African-born Dutch woman and had two daughters, and eventually returned to Pakistan to persuade its leaders that he could help them build a nuclear weapon — a national obsession — to counter nuclear rival India.
A towering man, Khan's outsized personality helped him win supporters.
"He's a very good conversationalist. He has a lot of wit," ur-Rehman said.
Khan was driven by a desire to empower Islam, which he saw as the only faith without a nuclear punch, and he became the architect of the first Islamic bomb.
"He thinks the whole world is against Pakistan, against Muslims getting empowered. That is his mental makeup," ur-Rehman said.
Other observers see less charitable traits at work.
"Khan is a braggart and a liar. He wouldn't have been successful if he weren't those two things," said David Albright, a physicist and proliferation expert who heads the Institute for Science and International Security, an advocacy group in Washington.
A member of Khan's extended family, who spoke on condition of anonymity lest he face reprisals, described the 71-year-old scientist as in fairly good spirits and recovering from prostate surgery in September. After a recent encounter, he said that Khan complained only of "a little leg pain."
Khan isn't a virtual prisoner. Six to eight friends are allowed regular visits with him, his wife, Henny, and a granddaughter who lives with them, several acquaintances said. Khan also is permitted to visit Karachi on occasion to see his siblings.
If the armed forces sponsored Khan's network, that may be why Musharraf's regime is so eager to keep him silenced, some analysts said.
"There are reports that he has already prepared a manuscript which he's given to his daughter to release if anything happens to him. There are also reports he's made a video," ur-Rehman said. "It would exonerate him from the allegation that he did it alone and he did it for money."
In his extensive interviews with Khan, ur-Rehman said, he learned such things as the identity of the fourth country — never identified — to which Khan and his supporters sold nuclear secrets. He declined to identify the country.
"This is something I can't write or talk about," he said. "I am frightened."
Some of Pakistan's highest-ranking retired military officers, among them strong nationalists with long-standing ties to Islamic militants, are pressing for Khan to be set free, saying that Pakistan has the right to sell nuclear know-how to anyone it pleases and can be open about it.
"We never signed the NPT (nuclear Non-Proliferation Treaty). We don't belong to the NPT. Why are they arm-twisting us?" said retired Lt. Gen. Hamid Gul, a former intelligence chief who helped arm the Taliban to fight the Soviet Union in neighboring Afghanistan.
Ur-Rehman said Khan had too much knowledge ever to walk freely again.
"I think he won't come out alive from his detention," he said. "His story is so revealing that he won't be allowed to come out."