Khalid Sheikh Mohammed - BBC Profile
Khalid Sheikh Mohammed - described by US intelligence as "one of history's most infamous terrorists" - has admitted being responsible "from A to Z" for the 11 September 2001 attacks on the United States, according to the Pentagon.
He also confessed to a role in 30 plots other than 9/11 including planned attacks on Big Ben and Heathrow airport in London and the beheading of US reporter Daniel Pearl in Pakistan in 2002, according to a transcript of his hearing at Guantanamo Bay.
He was believed to be the number three al-Qaeda leader before his capture in a safe house in Pakistan in March 2003. He was held in US custody at an undisclosed location from then until his transfer to Guantanamo Bay in 2006.
Born in Kuwait of Pakistani extraction, Khalid Sheikh Mohammed claims to have joined the Muslim Brotherhood at the age of 16.
After graduating from college in the US, he went to Afghanistan to participate in the anti-Soviet jihad. It was there that he is believed first to have met Osama Bin Laden.
He went to the Philippines and was implicated in the plot to blow up US airliners over the Pacific in 1995, known as Operation Bojinka.
Conspiracy. Murder in violation of the law of war, attacking civilians, attacking civilian objects, intentionally causing serious bodily injury, destruction of property in violation of the law of war, terrorism and providing material support for terrorism
Hijacking or hazarding a vessel
He features prominently in the US 9/11 Commission Report on how the 11 September 2001 attacks were carried out. His testimony was also used by defence lawyers for Zacarias Moussaoui, jailed for life in 2006 for his role in the plot.
Khalid Sheikh Mohammed helped build close operational ties between al-Qaeda and the shadowy militant group Jemaah Islamiah (JI) in south-east Asia, according to US intelligence.
By late 2001 he had become external operations chief for al-Qaeda and was involved in plots targeting Britain and the US, the Pentagon says.
Pakistani President Pervez Musharraf has alleged that he also helped lay the groundwork for the 7 July 2005 bombings in London.