First, I don’t know anything about FBI procedures as they would apply to Kavanaugh allegations.
Question, is it the FBI’s job to dig as far as this former Scalia law clerk has concerning possible mistaken identity?
The FBI's job is to investigate Federal matters. It's debatable whether the things nutjob Ford has described even rise to violations of state or local laws.
A kid trying to get a girl's top off, failing and quitting when she runs away doesn't even sound like sexual assault to me.
But how could any agency on earth investigate when she doesn't know when, doesn't know where, has no witnesses and has no physical evidence? Maybe the Maryland Bureau of Psychic Investigators could hold a seance and call up the past from a third of a century ago!?