The notion of terrorist organizations using nuclear weapons (especially very small ones, such as suitcase nukes) has been a threat in American rhetoric and culture. It is considered plausible that terrorists could acquire a nuclear weapon. In 2011, the British news agency, the Telegraph, received leaked documents regarding the Guantanamo Bay interrogations of Khalid Sheikh Mohammed. The documents cited Khalid saying that, if Osama Bin Laden is captured or killed by the Coalition of the Willing, an Al-Qaeda sleeper cell will detonate a "weapon of mass destruction" in a "secret location" in Europe, and promised it would be "a nuclear hellstorm" (Wikipedia, 2011).
In June 2002, U.S. citizen Jose Padilla was arrested for allegedly planning a radiological attack on the city of Chicago; however, he was never charged with such conduct. He was instead convicted of charges that he conspired to "murder, kidnap and maim" people overseas.
In November 2006, MI5 warned that al-Qaida were planning on using nuclear weapons against cities in the United Kingdom by obtaining the bombs via clandestine means.
In June 2007, the Federal Bureau of Investigation released to the press the name of Adnan Gulshair el Shukrijumah, allegedly the operations leader for developing tactical plans for detonating nuclear bombs in several American cities simultaneously.
The Alexander Litvinenko poisoning with radioactive polonium "represents an ominous landmark: the beginning of an era of nuclear terrorism," according to Andrew J. Patterson. Security specialist Shaun Gregory argued in an article that terrorists have attacked Pakistani nuclear facilities three times in the recent past; twice in 2007 and once in 2008.
After several incidents in Pakistan in which terrorists attacked three of its military nuclear facilities it became clear that there emerged a serious danger that they would gain access to the country’s nuclear arsenal, according to a journal published by the US Military Academy at West Point] In January 2010 it was revealed that the US army was training a specialised unit "to seal off and snatch back" Pakistani nuclear weapons in the event that militants would obtain a nuclear device or materials that could make one. Pakistan supposedly possesses about 80 nuclear warheads. US officials refused to speak on the record about the American safety plans.
A study by Belfer Center for Science and International Affairs at Harvard University titled 'Securing the Bomb 2010', found that Pakistan's stockpile "faces a greater threat from Islamic extremists seeking nuclear weapons than any other nuclear stockpile on earth".
According to Rolf Mowatt-Larssen, a former investigator with the CIA and the US Department of Energy, there is "a greater possibility of a nuclear meltdown in Pakistan than anywhere else in the world. The region has more violent extremists than any other, the country is unstable, and its arsenal of nuclear weapons is expanding."
Nuclear weapons expert David Albright author of 'Peddling Peril' has also expressed concerns that Pakistan's stockpile may not be secure despite assurances by both Pakistan and U.S. government. He stated Pakistan "has had many leaks from its program of classified information and sensitive nuclear equipment, and so you have to worry that it could be acquired in Pakistan,"
A 2010 study by the Congressional Research Service titled 'Pakistan’s Nuclear Weapons: Proliferation and Security Issues' noted that even though Pakistan had taken several steps to enhance Nuclear security in recent years 'Instability in Pakistan has called the extent and durability of these reforms into question (Wikipedia, 2011).