Huck: You wouldn't be suggesting that there's a conspiracy because of the FBI being involved are you?
The NTSB would investigate any aircraft incident/accident occuring in US territories. If it occurs to a US registered A/C in another country then they may run an investigation at the other countries request or provide a liaison officer to the investigation team. If the incident/accident results from a criminal act (or even suspected to have), then the FBI are responsibe for the investigation and the NTSB would provide specialist investigators to assist them.
No conspiracy here me thinks...