A man who looked what he was: a scientist with a calm, patient manner

In his years as a weapons inspector in Iraq and Russia, David Kelly was used to facing pressure.

A highly proficient microbiologist, he had travelled to Iraq 37 times as a member of the United Nations Special Commission (Unscom) tasked with tracking down and destroying Saddam Hussein's chemical, biological and ballistics weapons programmes.

In those visits, Dr Kelly built up a reputation for his thoroughness and patience, unfazed by the often aggressive attitude of Iraqi officials, waiting for them to calm down before proceeding with his questioning.

His appearance helped. Quiet, bearded, bespectacled, often unfashionably dressed, he looked what he was, a scientist. This often led the people he was investigating to underestimate him, something for which, he used to say, he was always grateful.

Within Unscom and the intelligence community, Dr Kelly became known as a safe pair of hands. This confidence in him led to one of Unscom's biggest breakthroughs. In January 1995, at the home of a Canadian colleague in New York, he met an Israeli military intelligence officer who disclosed that British and German companies had exported 32 tons of bacteria growth medium to Iraq. Following that trail led to important discoveries of hidden biological programmes.

The same confidence in his ability led to Dr Kelly being asked by the Secret Intelligence Service (MI6) to debrief a Russian defector, Vladimir Pasechinik in 1989.

Under Dr Kelly's questioning, Mr Pasechinik, director of the Institute for Ultrapure Biological Preparations in Leningrad, disclosed the full extent of Russia's biological programme.

Later Dr Kelly was part of an international team that inspected the Vektor biological plant near Novosibrsk in Siberia in January 1991. It discovered that the Russians were working on a weaponised smallpox programme. His fellow team members recall how Dr Kelly was the only one who picked up a strand during a conversation with a researcher and gradually teased out details of the programme.

Characteristically, he refused to gloat about this when talking later to journalists. "It was a sort of lucky break," he would say.

Garth Whitty, a former Unscom inspector, said: "Everything I know about him suggests he was highly professional, hard working, and a person of integrity. He was very, very focused and had a wealth of experience."

But Mr Whitty thinks that would not have equipped Dr Kelly for the ruthless realpolitik he found himself involved in. "I don't think anything he had done would have prepared him for the pressure of the last few days," he said.

In the past few years, Dr Kelly had eased off from his work. He seemed to be more relaxed, saying he was seeing more of his family - his wife, Janice, and his daughters, Sian, 32, and twins Rachel and Ellen, 30.

He took to visiting his local pub in the village of Southmoor, in Oxfordshire, for a quiet drink with his wife and, sometimes, his daughters.

But all that was about to change for ever. Dr Kelly's last days were spent in turmoil - a haunted figure who felt he had been betrayed; convinced that a reputation built up by years of dedicated service to his country lay in tatters.

His family and colleagues knew that he was deeply upset at being named by Downing Street and government ministers as Andrew Gilligan's informant in the story about Alastair Campbell and the "sexed up" dossier. What they did not realise was the depth of his despair.

Yesterday morning, as she waited for news, Dr Kelly's wife recalled how he had returned from his session before the Foreign Affairs Select Committee physically sick, suffering from acute stress mixed with anger.

It had not been a successful appearance. A calm and lucid start, in which he had explained why he could not have been the BBC mole, degenerated into unease and indecisiveness. At the end he had been cleared of being the informant. He was a "patsy ... just chaff", they said, who had been set up by the Government - something Dr Kelly himself had begun to believe.

There was anger among his friends and acquaintances yesterday. The landlord of his local pub, Steve Ward, said: "We are totally devastated. Sadly, since the story broke, it is pretty obvious that the Government was trying to find a scapegoat. He was always so happy with his family. I cannot think anything else that could have contributed to that."

There was also bitterness among his colleagues in Whitehall. One said: "What has happened is a disgrace. David came forward for the best of reasons, to help. They hung him out to dry. They destroyed this decent and honest man ... It was hardly a great secret that he sometimes spoke to journalists."

Dr Kelly was in demand among journalists because he was keen that we should not misunderstand or mistranslate complex technical matters. He had the ability to explain such matters simply.

According to his colleagues, Dr Kelly had no idea of what was going to happen to him when he came forward to "clear up the Gilligan matter" and explain why he could not be the mole.

The Government, beleaguered by accusations of manipulating intelligence on Iraq, had at last found a way to get back at the BBC. For four days Dr Kelly was subjected to interrogation that has been described as "brutal". He was threatened with prosecution under the Official Secrets Act, and told that his working life would be over unless he co-operated.

Despite his denials, and promises that his identity would be kept secret, officials - believed to be from Downing Street - gave his name to the media. Twenty four hours later, a No 10 spokesman publicly stated that he was the chief suspect.

Even after the Foreign Affairs Select Committee had cleared him, there was no respite. The ultra-Blairite minister Ben Bradshaw declared that unless the BBC formally denied it, Dr Kelly would remain the suspect.

Last night amid the shock, accusations and recriminations, and the Prime Minister's swift order of an independent judicial inquiry, one thing was very clear - Dr Kelly's death will haunt the Government for a long time.