The source said Thursday that federal investigators are "going down every rat hole," and that the FBI crew investigating "is not yet finished digging."
The federal probe, which began before Jackson took medical leave from Congress on June 10, first looked at activity in the congressman's campaign fund. But it has since gone into other areas, said the source, who would not elaborate.
Broad, sweeping subpoenas were issued in the Jackson investigation, including on financial institutions that controlled Jackson accounts both in and out of Washington, D.C., the source said.
Sun-Times columnist Michael Sneed reported last week that Jackson is in the midst of plea discussions. "No one has pled guilty, but plea discussions are ongoing," a source told Sneed.Meanwhile, investigators are also examining what role the congressman's wife, Ald. Sandi Jackson (7th), played in the finances, but the source described the inquiry into her so far as a "normal" part of investigating a main target.
Sun-Times first reported last month that the FBI in the Washington, D.C., field office had been investigating Jackson due to alleged "suspicious activity" in his finances.
The revelation came after Jackson checked into the Mayo Clinic, saying he suffered from bipolar depression. His 2nd District constituency, which includes some of the poorer areas of the city, has gone without representation since June.
Jackson has missed the first days of this week's lame-duck session in Congress and people close to him say they don't think he's ever returning.
Jackson was temporarily back in Washington last month when he was spotted at a nightclub drinking with other women. He returned to the Mayo Clinic but was again released, the facility said Tuesday.
People close to Jackson said he is still getting treated on an out-patient basis.
Jackson did not campaign for reelection and still coasted to victory on Nov. 6.