PO'ed P.I. Sues R. Kelly

That pesky child porno case is rearing its ugly head again for R. Kelly.

Kelly is being sued by a private investigator who claims the singer stiffed him on a $300,000 bill. According to a lawsuit filed last week in Missouri federal court, Charles Freeman claims he was hired during Kelly's trial to "obtain and/or recover certain tapes that were said to incriminate" R. Kelly.

Freeman said he did the job, but never got paid. He's suing for damages plus interests and costs.