His raging hatred for the West, in a video justifying the London suicide bombings, has made him seem the most transparent of the four men who detonated bombs in rucksacks and killed 52 others on 7 July.
But Mohammad Sidique Khan's extraordinary and rapid transition from law-abiding citizen to terrorist is revealed in documents showing he used to work for the Department of Trade and Industry (DTI), helping promote British firms overseas. He also helped Leeds police deal with confrontations between rival gangs of youths.
Leeds education authority's personnel file on Khan, obtained by The Independent under the Freedom of Information (FoI) Act, shows details of his work for the DTI's export arm in Yorkshire in the mid-1990s, when Britain was seeking more trade links with Asia.
But the investigations reveal that Khan lied on his CV about the seniority of his role at the DTI, which escaped the Leeds primary school that hired him on the basis of it. But he did help in the government-led drive to get more trade missions off the ground between 1995 and 1996.
Khan prospered as a primary school learning mentor, and his file provides the first real sense of the charisma and empathy with young people which enabled him ultimately to recruit fellow suicide bombers Shahzad Tanweer and Hasib Hussain. But it also charts his sharp decline from 2003. Prolonged absences from school - when it is now known he was visiting Pakistan - were followed by an unexpected failure to return from extended sick leave in 2004.
He was told his pay was being stopped and he sent an undated typewritten letter to the headteacher, Sarah Balfour. "I'm sorry I've not been in touch for a while," he wrote. "A lot has happened in the last few months. There is no definite timeframe to when I will return. We are returning next week. Unfortunately this is a letter of resignation from my post."
Before Khan took his job with the DTI in August 1995, he had been on a trip to the US. Friends said he came back with cowboy boots and a leather jacket, telling his contemporaries he wanted a career in the US. He became an administration assistant with the Benefits Agency, which he said was dull. The DTI offered better prospects.
John Major's Conservative government had just published its Competitiveness White Paper which committed the DTI to boost overseas trade, in Asia among other places. Khan's role did not include "monitoring security" for visits by exporters to overseas British embassies, as he said on his CV. But his fluency in Urdu and Punjabi may have made him optimistic about his prospects of moving beyond his relatively lowly position.
Khan left to study at Leeds Metropolitan University in September 1996, and took a 2:2 in business management, his file reveals. He clearly believed his vocation lay in steering disenchanted youths away from crime. He took paid youth and community work from Leeds council while finishing his degree and juggled a job at a petrol station in Ilkley, West Yorkshire.
The youth work was for a Saturday club affiliated to Leeds Community School, itself linked to the Iqra bookstore where police later found DVDs glorifying terrorism.
He wrote on his school job application: "As a youth worker I have had extensive experience in managing difficult children. I was approached by a member of the community who told me in confidence [that] his younger brother had been suspended from school and his parents were extremely upset. I began ... a discussion with the child [and] met his parents at their house and the situation was [resolved]."
Khan also detailed a "potentially dangerous" confrontation at a school. "I have an excellent rapport with the youth [community] so ... I targeted the ringleaders and spoke to them, calming them down and offering sympathy as well as empathy.
"We then approached the teachers and as a large group casually walked together up Beeston Hill which [defused] the situation." Associates of Khan have confirmed his role as an interlocutor between police and youths.
Khan also described his interventions in the case of a young heroin addict, his help in getting excluded children back into school and how he arbitrated in a dispute between rival gangs. "I feel patience and understanding comes through experience and maturity," he wrote. "I constantly analyse society and speak to people regarding current issues. I consider my ability to empathise with others and listen to their problems as well as offer viable solutions to be one of my strong assists."
Hillside Primary was obviously impressed, giving Khan several extensions to an initial £200-a-month contract. He also drove the school minibus.
Mrs Balfour, wife of the Labour MP John Trickett, valued him and allowed him paid special leave. "He was great with the children and they all loved him," she has said. "He did so much for them, helping and supporting them and running extra clubs and activities."
Khan's handwritten notes, which seem to be a part of his appraisals, reveal more. "I'm energetic, I [look for a] way of bettering things," he wrote. "Can build up trust and rapport with disillusion, understanding and empathy."
Khan clearly became disenchanted with the modest form of Islam practised by his father, Tika Khan, and stepmother, Mamida Begum. But in 1999 he had started frequenting the mosque. His file shows the process to radical Islam had started by 2002, a year after he joined Hillside. He began taking leave on religious grounds.
He took more than two weeks in January/February 2002 for "Muslim religious obligation, Haj, pilgrimage" and a similar period for "religious observances" the next year. From November 2003, he took 18 months, costing his employer an estimated £6,000.
But the sharp decline came in September 2004 when he was signed off sick, first for three days, then a further 10 days, a further three weeks and another three weeks. He is believed to have cited depression.
On 9 December 2004, after 10 weeks of absence began, Mrs Balfour told her personnel department in an "urgent" memo: "Sidique Khan should have provided the school with a sick note from November 22. Despite several letters reminding him of the school's sickness-reporting procedures he has failed to provide a sick-note. I request you to stop [his] pay."
Three days before, Khan had flown to Pakistan via Istanbul with Shahzad Tanweer. A week later, they took a train to Lahore then Faisalabad, and disappeared, Pakistani security officers said. They surfaced in Britain on 8 February.
MI5 believes they met Muslim extremists during the visit. Khan died, killing seven others, when he detonated his bomb at Edgware Road station on 7 July.
The life of Mohammad Sidique Khan
* October 1974 Born, Leeds
* 1994 Works first for Benefits Agency, then DTI (1995), then learning mentor at Hillside Primary (2001)
* 2001 Upsets father and stepmother by marrying a girl of Indian-Muslim descent, Hasina Patel, whom he met at Leeds Metropolitan University
* 2003 Establishes gyms in Beeston, radicalising young British Muslims. Periods of absence from Hillside
* July 2004 Introduced to government minister Hilary Benn during school tour of Commons. Is also subject of routine MI5 threat assessment after his name crops up in an investigation; check not pursued
* September 2004 Begins long sick leave
* November 2004 Travels to Pakistan with Tanweer to prepare for London attacks
* July 2005 Bombs Edgware Road Tube stationReuse content