To his colleagues and friends he was a quiet, devout family man who did a juggling act at community events and played the piano in church. Yet to the FBI agents grappling with one of America’s most sinister criminal mysteries, Dr Bruce Ivins was a mass murderer whose obsession with anthrax led to a tragedy.

When Ivins, 62, committed suicide at his Maryland home last week, he may have been only days away from arrest as the madman responsible for a series of anthrax attacks that terrorised America in the weeks after the September 11 attacks of 2001.

His death, and the subsequent revelation that he was about to be charged with murder and could have faced the death penalty, appeared to end one of the most frightening and controversial episodes in American criminal history.

The search for the culprit behind the anthrax-contaminated letters that killed five people, paralysed the US postal service and dumbfounded the administration of President George W Bush had taken seven years - with one disastrous wrong turn - and, it emerged yesterday, almost ended with a very different catastrophe.

As an FBI net closed on Ivins last month, he bought a gun and a bulletproof vest and boasted that he was “going out in a blaze of glory”, according to court documents. A social worker who heard his threats told a Maryland judge that “he was going to take everybody out with him”.

Ivins was later placed in psychiatric care and barred from visiting his offices at the US Army Medical Research Institute of Infectious Diseases at Fort Detrick, Maryland.

Having for years pursued a different suspect at the Fort Detrick laboratory, federal investigators had finally zeroed in on Ivins as the one scientist with both the technical knowledge and the access to anthrax spores who could have carried out the attacks.

Prosecutors believe that he posted anthrax samples in a deluded attempt to attract attention and research funds to what he believed was a neglected field of bio-defence study.

It also emerged yesterday that Ivins held several patents on genetically engineered anthrax vaccines that might have made him rich after a contamination crisis. His suicide came a month after the US government paid out almost $6m (£3m) in compensation to Dr Steven Hatfill, another government scientist from the same laboratory, whose career was destroyed when the FBI wrongly targeted him as the prime suspect for the anthrax letters.

The sudden turnaround in the long-stalled investigation shocked many of Ivins’s colleagues, some of whom claimed that the government had made another mistake and had harassed the scientist into suicide.

Ivins, an acknowledged anthrax expert who lived modestly on a civil service salary, was not at first suspected of involvement, not least because he assisted in the investigation of the crimes he was later accused of committing.

The anthrax attacks of 2001 prompted a surge of Pentagon spending on possible vaccines for troops, and Ivins’s career was transformed as he suddenly became a key figure in a high-priority defence programme. He wrote 14 academic papers in the past seven years on possible anthrax treatments and vaccines.

It is not yet clear exactly when prosecutors began to suspect him, but US media reports focused yesterday on a series of accidental contaminations at his laboratory in late 2001 and early 2002. Ivins appears to have given misleading accounts of what occurred but did not trigger suspicion until much later.

The exoneration of Hatfill on June 27 triggered a sharp decline in Ivins’s mental state. He had already been treated for depression and lawyers said the Hatfill deal opened the door for the FBI to bring charges against a different suspect.

After seeing a psychiatrist, Ivins began attending group therapy sessions. Jean Duley, the social worker leading the session, was so alarmed by the scientist’s behaviour that she sought a restraining order against him.

At a court hearing Duley said that she regarded him as a “revenge killer . . . when he feels that he has been slighted he plots and actually tries to carry out revenge killings”.

All this shocked Ivins’s friends, one of whom accused the FBI of hounding him to his death. Yet a different picture emerged from his estranged brother, Tom, who told reporters he was not surprised to learn that Ivins had been making death threats. “He considered himself like a god,” the brother said.

Last month at one of his counselling sessions Ivins threatened to slaughter his colleagues at work. He was later detained, committed to a psychiatric hospital for observation and barred from returning to Fort Detrick.

He was eventually allowed home and last weekend was found unconscious on his bathroom floor after swallowing an overdose of painkillers. He died in hospital on Tuesday.

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