"The FBI is now conducting further forensic examination for the purpose of identifying trace evidence, residues and signatures of production that could provide evidence to support the investigation, " the agency said.

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"The FBI is now conducting further forensic examination for the purpose of identifying trace evidence, residues and signatures of production that could provide evidence to support the investigation, " she said in a news release.

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That did not surprise the Capitol's attending physician, Dr. John Eisold, who said there was no evidence that the trace spores posed a public health risk.

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And a member of his staff supervised that personally to make sure that that happened, leaving no possible trace of e-mail evidence or other what - other things that he left behind.

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The unexploded bomb left crucial evidence intact that detectives used to trace Mr Shahzad.

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