CNN  —  A federal grand jury has been regularly convening in the continuing criminal investigation into music mogul Sean “Diddy” Combs, three sources told CNN. Jurors on Thursday were expected to hear from a witness who claims he is in possession of videos that allegedly contain footage of celebrities potentially being victimized by Combs, one of the sources said. Attorney Ariel Mitchell told CNN that one of her clients was summoned to testify in front of the grand jury on Thursday. This client,