You outline how an investigation is done. Persuade me how the FBI can magically verify a story that doesn't have a location, a date, a time, details before the incident, details after the incident, and there are only 4 persons involved, 3 of which say it is false, and only the accuser says it is true, but has no details, just a story. You give a good road map for how an investigation can be made, and then I'll tell you if it makes sense to stall the vote so it will happen.
Like I've said, let the local authorities investigate. They actually have jurisdiction. The FBI does not. No federal crime is alleged.