Updated

Saying its original investigations were incomplete, the FBI plans this week to go back inside an anthrax-contaminated building owned by tabloid publisher American Media Inc., where an employee was fatally infected last fall, officials said Monday.

In the first search of the building since it was quarantined and sealed last fall, agents will use newly developed techniques to search for anthrax spores and other evidence throughout the building.

Previous searches inside the building concentrated on a mailroom and workstations used by infected employees.

"We hope this investigation will bring to justice the person or persons responsible for this horrific act," said Hector Pesquera, the FBI's special agent in charge of the Miami division.

Pesquera said the two-week operation inside the building should be under way by Wednesday. Investigators moved mobile units into the building's parking lot Monday in preparation, said Boca Raton police commander Maria Maughan.

AMI has had to use other offices in the area to publish its six supermarket tabloids, including The National Enquirer, Globe and Weekly World News.

The building has been under federal quarantine since October, when photo editor Robert Stevens died after becoming infected at his desk. He was the first person and only Floridian to die during the anthrax attacks last fall, which killed five people. Another AMI worker became ill and was hospitalized for more than three weeks.

Spores delivered by mail also hit media outlets in New York and a congressional building in Washington.

While transmission by mail was suspected at AMI, investigators never determined how anthrax spores entered the building. The original investigation did not locate a "dissemination device" or large quantities of spores.

Pesquera said workers would collect "thousands and thousands" of new samples in the search for the source of the spores and how they were disbursed in the building. He would not elaborate on the new techniques to be used.

"We're looking for a dissemination device such as a letter or letters, again, to generate new leads," said Dr. Dwight Adams, assistant director of the FBI's laboratory division.

He said investigators hoped to do a full assessment of any contamination throughout the building and the mailroom and to compare spores with infected letters mailed to Sens. Patrick Leahy of Vermont and Tom Daschle of South Dakota.

Sen. Bill Nelson, D-Fla., said last week he would introduce legislation to require the federal government to help decontaminate the building, fearing a hurricane could spread spores. The legislation would allow the federal government to take over the building and use it as a laboratory to study anthrax. AMI executives, who are unable to clean up the building on their own, have offered to give the building to the government.

The fenced, guarded building has stood vacant since employees evacuated one hurried Sunday afternoon in October. David Pecker, the company's CEO, said front pages from the Oct. 4 editions are still plastered to the walls, and coffee cups, fish tanks and family photos are scattered across employees' former desks.

Employees could take nothing from the infested building. But one executive has been allowed to don a moon suit and enter the building at least a dozen times, most recently in March when he tried unsuccessfully to recover the company's database of 500,000 photos.