In response to the FBI briefing that lawmakers received on the developments surrounding the anthrax investigation, Sen. Chuck Grassley (R-Iowa) sent a letter requesting more information about the government’s findings.

In the Aug. 7 letter sent to both FBI Director Robert Mueller and Attorney General Michael Mukasey, Grassley asked 18 different questions, including one inquiring why the government had not acted sooner when it learned that Bruce Ivins, the Army scientist who investigators say is responsible for the anthrax tragedy, suffered from mental health issues. It also questions whether Ivins received a polygraph and if not, then why.

“When did the FBI first learn of Dr. Ivins’ late-night activity in the lab around the time of the attacks? If this is powerful circumstantial evidence of his guilt, then why did this information not lead the FBI to focus attention on him … much sooner in the investigation?” Grassley asked.

Grassley, a member of the Judiciary Committee and whose personal office sits in the Senate office building that was hit by the anthrax attacks in 2001, has also called for hearings into the federal investigation.

According to a spokeswoman for the Iowa Republican, Grassley believes that the FBI “kept Congress out of the loop for a very long time” and he wants to know what evidence there is to implicate a single individual for the entire case. The aide added that the letter serves as the first step in getting some of those answers.

“This has been a long investigation full of missteps and mistakes. There’s been too much secrecy up to this point and it deserves a full and thorough vetting,” Grassley said in a statement. “There are clearly a lot of unanswered questions and it’s time to start a dialogue so we can get answers.”