A heart problem, a battle to save his reputation, the glare of publicity. What did drive Dr Kelly to suicide?

Dr David Kelly was a sick man. The 59-year-old scientist was suffering from a "significant degree" of coronary heart disease when he set off for his fateful walk in the Oxfordshire countryside on 17 July.

When he reached the place of his chosen end, in a "deliberate act of self-harm" he methodically removed his wristwatch and spectacles before slashing his left wrist.

He was found dead by police in the field near his home at 9.20am the following day.

The Home Office pathologist Dr Nicholas Hunt, who carried out the post-mortem examination on Dr Kelly's body, found attached to the dead scientist's chest four electrocardiogram pads.

The pathologist said that heart disease may have played some small part in the rapidity of death but was not the major cause.

As Lord Hutton convened the opening session of his inquiry into his death it was Kelly the man that dominated yesterday's proceedings.

What emerged was a public servant battling to minimise the damage done to his distinguished career by his unofficial briefing with the BBC journalist Andrew Gilligan.

The reporter's actions, he apparently felt, had put in jeopardy the assignment that Dr Kelly valued most - the opportunity to lead the British survey team in the crowning moment of a career whose latter years had been spent successfully tracking down Iraq's weapons of mass destruction.

He had told others in his closely knit international community of biological experts that he was looking forward to returning to Iraq. Yesterday those within that community were still mystified by the suicide of their eminent colleague.

"What was going round in David's brain? Why did he feel he had no other course? All of my colleagues who knew David, none of us understand," says the Australian Rod Barton, one of the self-described "gang of four" biological experts who worked with Dr Kelly in the 1990s in Iraq.

These were the men who reduced the notorious "Dr Germ" - the top bio-weapons scientist Rihab Taha - to tears.

In 1994, the four were virtually starting from scratch, and were not convinced that Iraq even had a germ warfare programme. But their robust questioning of Iraqi scientists - led by Dr Kelly - finally "cracked the code" and forced the Iraqis into owning up to an offensive programme in July 1995. For this achievement alone, according to Dr Kelly's former boss Rolf Ekeus, they deserved a Nobel prize for arms control, if there were such an award.

Mr Barton said: "He's not the sort of person to take his own life. He was used to pressure from his work in Iraq."

Dr Richard Spertzel, the top US expert who headed the UN biological weapons team, admits that the four - himself, Dr Kelly, the Briton Hamish Killop and Mr Barton - were known as the "grumpy old men" - "We wouldn't take any nonsense," he says.

Dr Kelly's methodical interviewing technique, during his 36 missions to Iraq from 1991 to 1998, is what his colleagues remember best, particularly his interviews of Dr Taha, whom he baptised the "desert rose". "None of us called her Dr Germ, that was a newspaper invention. In fact I apologised to her for that," says Dr Spertzel.

Mr Barton said: "David would say, "Let's start at the beginning - and we knew we were going to interview this person for hours and hours.

"I sometimes thought he was too aggressive.The Iraqis would tell us a story. David would say, 'I don't find that credible.' That meant they were lying."

Dr Kelly's polite understatement would provoke an explosive reaction from the Iraqi side. On more than one occasion, Dr Taha stormed out of the room, or burst into tears, in a diversionary tactic aimed at sowing confusion among the inspectors.

"Kelly and Spertzel were so embarrassed, they weren't used to women crying," Mr Ekeus recalls.

By 1996-97, the biological weapons team had reached an impasse with the Iraqis, who had still failed to account fully for their anthrax stockpiles, delivery systems and germ warfare programmes.

Dr Kelly and Mr Barton were among the last inspectors with the Unscom team to pull out in 1998, before the US and UK bombed Iraq for failing to co-operate with the inspections. And Dr Kelly was among the first back inside the country after the second Gulf War, to work out arrangements for resuming the search for banned weaponry. The day after his death, he had originally been scheduled to join Hamish Killop in Iraq. "I was looking forward to working again with him. It didn't happen," says Dr Spertzel.