Brad Pitt will not be prosecuted for the incident on his private jet ... in fact, we've learned there was never an investigation in the first place because FBI sources say there's no case.
TMZ broke the story ... after the L.A. County Dept. of Children and Family Services started its investigation into allegations Brad struck his 15-year-old son on a private jet, the LAPD was notified and turned the matter over to the FBI, which has jurisdiction.
Well-placed law enforcement sources tell us the FBI never opened an investigation, and say the matter should never have even been referred to the agency.
The Bureau's official position is that they are still fact-gathering, though they are not calling it an investigation. Behind the scenes, we're told the case will go nowhere.