Despite some theories that the plane may have been the victim of sabotage , poor maintenance , or in-flight fire , investigators could not find Know enough evidence to support Supporting any definite conclusion .

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

Due to lack of definite evidence an open verdict was returned ; though the fireman of the coal train was censured Judgment_communication for not alerting Warning the signal box of the stationary train 's position as he was required Imposing_obligation to do under Rule 55 .