Scientists close to solving anthrax puzzle

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Scientists in a Maryland laboratory believe they may be on the verge of cracking the genetic sequencing of the anthrax spores used in one of the bio-terrorist attacks on American targets last year.

The work, which is being done at the Institute for Genomic Research in Rockville, Maryland, a few miles from Washington DC, could give investigators an important break in their search for the perpetrator of the attacks, which left five people dead and infected 13 others.

Specifically, researchers expect to identify genetic footprints in the preparation found in a letter sent through the post to American Media, a newspaper publisher in southern Florida, just after the terrorist attacks on 11 September. Similarly contaminated letters went to Tom Brokaw, a news presenter with NBC, and to Tom Daschle, the US Senate's majority leader.

Early in the investigation scientists realised that the spores came from so-called Ames anthrax, a form of the bacteria that was first isolated by the US Army in Ames, Iowa. Samples of Ames anthrax have found their way to laboratories around the world, including about 12 in America.

Distinguishing the anthrax used by the terrorist from other forms of Ames anthrax might allow investigators to identify exactly which of those US laboratories was the source of the spores sent through the post. They have long believed that the culprit lives within America and is an anthrax expert.

An announcement by the scientists is expected within the next couple of weeks and could even come by the end of this week. But there is no certainty that identifying where the anthrax came from will lead to the immediate arrest of a suspect. It has become clear in recent weeks that there has been little control at many of the US facilities over who can have access to their anthrax samples.

The FBI, which has had little success with its investigation so far, plans to hold a press conference later this week to announce it will increase the reward it is offering the public for any information that leads to the arrest of the perpetrator.

In Washington, meanwhile, American senators and their staff were allowed back into an office block on Capitol Hill that had been closed for three months to be decontaminated because of the discovery of the anthrax letter that had been sent to Senator Daschle.

Among those returning to the Senate Hart Building was the former vice-presidential candidate Joe Lieberman. "I go in with confidence and a prayer," he said.