The investigative arm of Congress will take another look at the science the FBI used to determine who mailed deadly anthrax-laced letters in 2001.

The Government Accountability Office has notified Rep. Rush Holt, a New Jersey Democrat, that the agency will review the science behind the FBI's conclusions that Army scientist Bruce Ivins sent the letters that killed five people.

The letters were mailed from a mailbox in Princeton, N.J., which is in Holt's district. The congressman has long maintained that the FBI's work on the case was shoddy and full of holes. The FBI concluded Dr. Ivins was a disturbed man who sent the letters while his laboratory faced the prospect of losing support for its anthrax vaccine program.

The National Academy of Sciences is in the midst of a two-year-review of the scientific work that led the FBI to finger Dr. Ivins after spending years chasing other suspects. Dr. Ivins took a fatal overdose of pills in 2008 as a federal grand jury prepared to indict him for the anthrax mailings.

In a letter to Holt, GAO officials said they would conduct their review once the NAS reaches its conclusions, which is expected later this year.