Among those to be closed are towers at regional airports in Frederick, Maryland, and near St.

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Hatfill once worked at the Army's bioweapons research lab at Fort Detrick in Frederick, Maryland.

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Investigators also traced the envelopes that contained the spore-laced letters to the Frederick, Maryland, area where Ivins lived, Taylor said.

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Gary Gilbert, from the US Army's Telemedicine and Advanced Technology Research Centre in Frederick, Maryland, said that the teddy bear appearance was deliberate.

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Ivins, 62, died at a hospital in Frederick, Maryland, where he was taken after he was found on a bathroom floor at his home.

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Williams and Malvo -- identified as Lee Boyd Malvo on his birth certificate -- were arrested early October 24 while sleeping in a car at a freeway on Interstate 70, several miles west of Frederick, Maryland.

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Frederick, Maryland (CNN) -- The Federal Aviation Administration on Friday told 149 regional airports across the country it would begin closing their air traffic control towers in April, but said it would spare another 40 towers that had been on the chopping block.

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According to a study carried out by Dr Landau, in co-operation with Marc Parmentier at the Free University of Brussels, and Stephen O'Brien at the National Cancer Institute in Frederick, Maryland, roughly one in every ten Caucasians carries it, although it is strangely absent in African and Asian populations.

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The District Court of Maryland at Frederick ordered Ivins on July 24 not to threaten harm to the woman, contact her, or enter her home or workplace.

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