Sources said the search is in connection with the investigation into former Fort Detrick government scientist Steven Hatfill, reports Stewart. The search is taking place in Gambrill State Park, several miles from Hatfill's old apartment.
An FBI press release stated that it was "conducting forensic searches on public land located within the city of Frederick.
"The searches are related to the FBI's investigation of the origin of anthrax-laced letters mailed in September and October 2001, which resulted in five deaths."
The search was taking place as the Justice Department defended its use of the term "person of interest" to describe Hatfill in the anthrax investigation, contending it accurately depicts his place in the probe and was not intended to cast suspicion on him.
In a letter to Sen. Charles Grassley, Assistant Attorney General Daniel J. Bryant said the term originated with "unnamed sources in the FBI" as speculation swirled in the media and on the Internet that Hatfill might be a suspect.
"The phrase was never used by the FBI or the Department of Justice to draw media attention to Dr. Hatfill," Bryant said in the letter. "On the contrary, the phrase was used to deflect media scrutiny from Dr. Hatfill and explain that he was just one of many scientists who had been interviewed by the FBI and who were cooperating with the anthrax investigation."
Hatfill has denied any involvement in the anthrax attacks, which killed five people and infected 18 others when letters containing the deadly spores were sent to government and news media offices in Washington, New York and Florida. Thousands more were put on preventative antibiotics as a precaution.
The Justice Department letter, released Thursday by Grassley, R-Iowa, acknowledged there is no formal definition for "person of interest," but said it is a commonly understood term for "an individual whom law enforcement officials seek to question in connection with a particular matter."
In a statement, Grassley said the Justice Department letter shows use of the term to describe Hatfill is unprecedented and not supported by any formal policy or evidentiary standard.
"Government agencies need to be mindful of the power they wield over individual citizens, and should exercise caution and good judgment when they use that power," said Grassley, a senior member of the Senate Judiciary Committee.
A separate letter to Grassley states that the Justice Department had the authority to demand that Louisiana State University stop using Hatfill work related to a government contract. Hatfill was fired by LSU on Sept. 3 after the Justice Department e-mailed the university to "cease and desist" using Hatfill as an expert or course instructor.
That letter, also from Bryant, states that the Justice Department has clear "managerial oversight and control" over such government-funded activities as the National Domestic Preparedness Consortium, of which LSU is a member.
The government, Bryant said, "may on occasion need to make a decision concerning which personnel" should work on such activities. The Justice Department, he added, did not bar Hatfill from continuing to work on a department-funded project so long as he was not an expert or course instructor.
Hatfill remains unemployed and is living in the Washington area, a spokesman for the scientist said this week.
Hatfill worked until 1999 for Fort Detrick's Army Medical Research Institute of Infectious Diseases in Maryland. It is the primary custodian of the virulent Ames strain of anthrax found in the anthrax letters.