>> there may have been back channels used by oligarchs to fund the trump campaign and perhaps the inauguration as well. >> reporter: cnn reported that mueller has pinpointed at least three russian oligarchs whose identity was unknown. one was stopped when his private plane stopped in the new york city area and agents searched their electronics. >> now mueller is looking at the oligarchs directly and interviewing them in an effort to understand from their point of view what happened here. so it's a widening net for mueller and a tightening noose for manafort. >> reporter: manafort has pleaded not guilty to criminal indictments in virginia and washington, d.c. stemming from the mueller probe. now cnn learned mueller is using information obtained during the