Frederick, Md. ? The FBI is considering draining a pond in Frederick Municipal Forest to search for evidence related to the 2001 anthrax attacks, Mayor Jennifer Dougherty said Sunday.

The plan stems from a new FBI theory reported Sunday by The Washington Post about how the person behind the attacks could have packed the deadly spores into envelopes without being infected or leaving traces in homes, buildings or on open land.

The theory is based on evidence recovered from the pond this past winter, the Post reported Sunday, citing anonymous sources close to the investigation.

FBI spokeswoman Debra Weierman, contacted Sunday, declined to comment on the Post report or on searches conducted at a series of ponds in the forest.

The attacks nearly 19 months ago killed five people and sickened 13 others. The pond findings offer physical evidence in a case that so far has been built almost exclusively on circumstantial clues, the Post quoted sources as saying.

Two sources familiar with the items recovered from one of the ponds described a clear box, with holes that could accommodate gloves to protect the user during work, the Post reported. So-called glove boxes are commonly used to handle dangerous pathogens.

For protection against airborne bacteria, a person could put envelopes and secured anthrax powder into the box, then wade into shallow water and submerge it to put the bacteria inside the envelopes, some involved in the case believe, the Post said. Afterward, the envelopes could have been sealed in plastic bags before being removed from the underwater chamber.

Other sources told the newspaper the work could have been done on land and the materials discarded in the pond.