The FBI responded by pointing out that the review panel asserted that it would not be possible to reach a definite conclusion based on science alone .
The FBI said that a combination of factors led the FBI to conclude that Ivins had been the perpetrator .
The FBI responded by pointing out that the review panel asserted that it would not be possible to reach a definite conclusion based on science alone , and said that a combination of factors led the FBI to conclude that Ivins had been the perpetrator .