A former director of the FBI's anthrax investigation says the agency is concealing evidence that casts doubt on whether an Army scientist sent the anthrax-filled letters that killed five people in 2001.

Richard Lambert made the assertion in a federal lawsuit filed earlier this month in Knoxville, Tennessee.

The FBI has said its conclusions were based on all the evidence it collected.

The scientist, Bruce Ivins, took his own life in 2008 as prosecutors prepared to charge him.

Lambert ran the investigation from 2002 to 2006, when he transferred to Knoxville. Now retired, he contends the Justice Department illegally got him fired from a security job because he had complained internally about mismanagement of the anthrax probe.

Under Lambert, anthrax investigators focused on another Army scientist, Steven Hatfill, who was eventually cleared.