Diddy is in big trouble.

He's been investigated by the Feds for sex trafficking.  And not just any Feds.  The Southern District of New York, which is known for its hard-charging, detail-oriented prosecutors.

Yesterday, US Weekly spoke to lawyer Neama Rahman who believes Diddy may be spending the rest of his days in prison.

"Under federal law, if a person is convicted of even one count of sex trafficking, it carries a minimum ten or fifteen-year prison sentence.  Minimum.  The judge can't go any lawyer for each count depending on the age of the victim ... I wouldn't be surprised if this is another Jeffrey Epstein or R. Kelly type case.  We are talking bout multiple victims across multiple jurisdictions over a significant period of time ... I wouldn't be surprised if Diddy is arrested in the coming days or weeks," Rahman said.

Rahman also believes Diddy did himself in by not settling with Cassie sooner.  Apparently, they were $10 million apart on a settlement, and that's why Cassie went public.  He believes if he had just given her the extra cash and she stayed silent, it may have not triggered the other lawsuits and the feds jumping in.