Khalid Sheikh Mohammed has long been the prime suspect as mastermind of the 9/11 attacks — but his candid confession will be regarded as a milestone in the fight against terror.

It raises the real possibility that al-Qaeda’s most ambitious planner, the man more responsible than anyone else for inventing the movement’s strategy of spectacular, no-warning, mass-casualty attacks, will finally provide details of the workings of the shady organisation.

In 1996 it was Sheikh Mohammed who came to Osama bin Laden with the idea of hijacking airliners over the United States and crashing them into iconic buildings. Bin Laden is said to have been deeply sceptical that the plan could work and Sheikh Mohammed spent months persuading him.

Within a month of the attacks, the US authorities publicly identified him as the planner and placed a $25 million price on his head. After his transfer from one of the CIA’s “ghost prisons” to Guantanamo Bay last year they described him as “one of history’s most infamous terrorists”.

In documents released by the White House at the time, Sheikh Mohammed was said to have “devoted most of his adult life to terrorist plottings, specifically against the United States”. He was further described as “the driving force behind the attacks on 11 September 2001 as well as several subsequent plots against US and Western targets worldwide”.

Those targets included London, where he had ambitions to attack Heathrow and blow up Big Ben. Richard Reid, the British shoebomber in prison in the US, was one of his recruits.

Sheikh Mohammed is believed to have been born in 1964 or 1965 in Kuwait but his family originated from the Baluchistan region of Pakistan. In the 1980s he went to study in the US and graduated in 1986 with a degree in mechanical engineering from North Carolina A & T State University. He then travelled to Afghanistan to fight with the Mujahidin against the Soviet occupying army; three of his brothers are thought to have died in the conflict.

It is thought that he first met bin Laden in the Pakistani border town of Peshawar around this time but did not immediately ally himself to the rich Saudi.

When the Soviets left Afghanistan, Sheikh Mohammed went to South-East Asia, where he made contact with Islamist groups. While there he devised the Bojinka plot, which envisaged blowing up 12 US airliners in-flight over the Pacific.

When that plan was thwarted and he was indicted in connection with it, KSM, as he became known in intelligence circles, disappeared. His familiarity with the West and use of 30 aliases enabled him to travel relatively untroubled, disguised as a businessman.

Sheikh Mohammed resurfaced in Afghanistan in 1999, when he recognised bin Laden as his emir, or leader, and became a senior figure in al-Qaeda’s command structure.

In 2000 Sheikh Mohammed sent a young British Muslim, Dhiren Barot, to the US to carry out reconaissance on potential targets including the World Bank, in Washington, and the New York Stock Exchange. When the security climate changed after 9/11, Barot was moved to London with orders to plan and execute an attack there.

He devised two plans that were sent back to Sheikh Mohammed and discovered on a laptop computer in Pakistan in 2004. Barot was jailed for life last year after pleading guilty to conspiring to commit murder.

KSM himself was detained in March 2003 when Pakistani police raided a house in Rawalpindi and found him asleep in an upstairs room. His whereabouts were then unknown until it was revealed that he and other high-profile al-Qaeda detainees had been moved to Guantanamo Bay.

The confession released last night is from a Pentagon transcription of hearings that began last Friday.

“I’m not happy that 3,000 were killed in America. I feel sorry even,” he said in the extracts, which were edited by US officials. “The language of any war in the world is killing.”

North Carolina student who invented hijack plot

— As a teenager he went to a Baptist school in North Carolina before going on to university there to study mechanical engineering

— After graduation in 1986 he drifted to Afghanistan to join the Muslim holy war against the Soviet invasion. He lasted three months before heading for a job with an electronics firm

— He was, the CIA says, a planner not an action man. He worked for the Qatar Government in its electricity headquarters, from where he shunted money to extremist groups

— He helped to fund the first attack on the World Trade Centre, in 1993, and joined a plot to kill Bill Clinton

— In 1996 he told Osama bin Laden his idea of crashing jets into several US buildings at the same time but bin Laden rejected it. Five years later, it happened, left

— He was arrested on March 1, 2003, in Rawalpindi, Pakistan

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