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In a bid to catch the anthrax culprit, the FBI has subpoenaed a dozen labs across the US, requiring them to send samples of their anthrax stocks to scientists investigating last year’s attack. Analysis of the samples could reveal the source of the bacteria used by the attacker, and the timing of the subpoenas could stem from the discovery of a section of the anthrax bacterium’s genome that might vary between stocks held by different labs (Â鶹´«Ã½, 2 March p 11). But the FBI says only that it delayed issuing subpoenas because it needed time to develop a legally watertight procedure for collecting the samples.