that a few people from the FBI entered the NTSB's hanger late at night for "reasons unknown." Did they masterfully alter the evidence so it would look like the result of a fuel tank explosion? How can we know? The documentary is only asking questions.
Or maybe the NTSB IIC (Investigator In Charge) didn't want law enforcement types interfering with his investigation and didn't allow the FBI unlimited access to the evidence. Maybe the FBI brass didn't like another federal agency telling them what to do, and decided to look at the evidence when the NTSB wasn't around. How can we know? I'm just asking questions.