It is the second time the Federal Bureau of Investigation (FBI) has searched the home of Dr Steven Hatfill, who lives near a military laboratory in Maryland.
An FBI spokeswoman said the investigation was continuing, but there had been no arrest.
Five people died and 13 others were infected when letters contaminated with anthrax were sent through the US postal system last year.
Search warrant
In the wake of the 11 September terror attacks, it was first suspected that Osama Bin Laden's al-Qaeda network was behind the attacks.
Investigators later said they thought the letters were the work of a domestic criminal.
When investigators first searched Dr Hatfill's home at the end of June he gave his consent, but according to FBI officials the new search was being carried out with a warrant.
Dr Hatfill worked at Fort Detrick, a US Army biological warfare research facility, about 65 kilometres (40 miles) north-west of Washington.
He also worked for the Army Medical Institute of Infectious Disease, America's centre for biological warfare defence research.
Dr Hatfill is one of about 20 US-based scientists being scrutinised as part of the investigation.
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