In early October 2001, Secretary of State Colin Powell visits Pakistan and discusses the security of Pakistan’s nuclear weapons with Pakistani President Pervez Musharraf. He offers US technical assistance to improve the security of Pakistan’s nukes, but Pakistan rejects the offer. Powell also says that the CIA learned of a secret meeting held in mid-August 2001 between two Pakistani nuclear scientists and al-Qaeda leaders Osama bin Laden and Ayman al-Zawahiri (see Mid-August 2001). As a result of US pressure, Pakistan arrests the two scientists, Sultan Bashiruddin Mahmood and Chaudiri Abdul Majeed, on October 23. The Pakistani ISI secretly detains them for four weeks, but concludes that they are harmless and releases them. [Tenet, 2007, pp. 264-268; Frantz and Collins, 2007, pp. 269-271] In mid-November, after the Taliban is routed from Kabul (see November 13, 2001), the CIA takes over the headquarters there of Ummah Tameer-e-Nau (UTN), a charity founded by the two scientists. In addition to charity material, they find numerous documents and pieces of equipment to help build WMD, including plans for conducting an anthrax attack. [Levy and Scott-Clark, 2007, pp. 322] As a result, on December 1, CIA Director George Tenet, Rolf Mowatt-Larssen, head of the CIA Counterterrorist Center’s WMD branch, and a CIA analyst named Kevin make an emergency trip to Pakistan to discuss the issue. Accompanied by Wendy Chamberlin, the US ambassador to Pakistan, Tenet meets with Pakistani President Pervez Musharraf and urges him to take stronger action against the two scientists and their UTN charity. Musharraf reluctantly agrees, and the two men are rearrested. According to a 2007 book by Tenet, after being tested by a team of US polygraph experts and questioned by US officials, “Mahmood confirmed all we had heard about the August 2001 meeting with Osama bin Laden, and even provided a hand-drawn rough bomb design that he had shared with al-Qaeda leaders.” During the meeting, an unnamed senior al-Qaeda leader showed Mahmood a cannister that may have contained some kind of nuclear material. This leader shared ideas about building a simple firing system for a nuclear “dirty bomb” using commercially available supplies. [Tenet, 2007, pp. 264-268; Frantz and Collins, 2007, pp. 269-271] However, on December 13, the two scientists are quietly released again. The US does not officially freeze UTN’s assets until December 20, and Pakistan apparently follows suit a short time later (see December 20, 2001). [Wall Street Journal, 12/24/2001; Frantz and Collins, 2007, pp. 271]