FBI Director Robert S. Mueller III said an independent team of researchers and engineers from the National Academy of Sciences will review the government investigation in the 2001 anthrax attacks, which killed five people after anthrax was mailed to media organizations and politicians in the US not long after the September 11 attacks on the Twin Towers. In addition to the five deaths, more than 20 other people were sickened.

Army scientist Bruce Ivins is the leading suspect in the 2001 anthrax attacks that frightened Americans. He had access to lethal substances and had worked with very hazardous pathogens and viruses in an attempt to improve the anthrax vaccine. Ivins had played a central role in research to improve anthrax vaccines by preparing anthrax formulations used in experiments on animals. But Ivins had also helped the FBI analyze the powdery material recovered from one of the anthrax-tainted envelopes sent to a U.S. senator’s Washington office.

Bruce Ivins, 62, who had worked for the past 18 years at the government’s elite biodefense research laboratories at Detrick, Md., committed suicide by taking a massive dose of Tylenol mixed with codeine just as the Justice Department was about to file criminal charges against him for the anthrax attacks.

But Bruce Ivins might not be the only suspect in the 2001 anthrax attacks. FBI investigators were very sure that Ivins was the person they were looking for, but the case still remains open. The FBI director said investigators had made a “clear identification,” tracing the deadly anthrax contained in a series of letters to the substance found in a vial controlled by Ivins. Investigators “eliminated every other person” who might have had the skills to produce the material, Mueller said.

The National Academy of Sciences is conducting an independent review of the FBI investigation. Mueller said the independent review will focus on “the scientific approach used during the investigation.”

Recently, authorities have unsealed a July 11 search warrant for Ivins’s work locker and lab space as well as a warrant to search a pair of computers in the Frederick public library that he used in late July, shortly before he took the overdose of Tylenol mixed with codeine.

Bruce Ivins’ attorneys said the scientist was innocent and emphasized there is no “concrete evidence” showing the scientist created the powdered anthrax and mailed it to media organizations and politicians after the September 11 attacks. Some lawmakers have also been skeptical of the government case against Ivins and several senators and House members have called for an independent investigation of the anthrax case, the San Francisco Chronicle notes.

“You can assume we looked at every laboratory in the United States and several overseas that had both the type of the Ames anthrax that we found in this case but also had the individuals capable of (processing the spores),” Mueller said, according to the same source. Mueller said he “would have to get back to (Nadler) on individual facilities” an laboratories with access to the kind of anthrax used in the attacks and how they were ruled out as investigators closed in on Ivins, the San Francisco Chronicle noted.

“For the time being, this case remains open while certain investigative activity winds up,” the FBI director said. More information will be released when the investigation is closed.