The investigation, I have learned, is following its usual process -- and that means the next step is sending written questions to Burris. While Durbin and Reid were interviewed by the panel in March, Burris has not yet been asked to appear before the committee, which started its work in February.

At issue before the panel are conflicting statements Burris made about conversations with ousted Gov. Rod Blagojevich -- and those close to him -- about his appointment.

A wiretap recently released by federal prosecutors in Chicago at the request of the ethics panel revealed a conversation Burris had with Robert Blagojevich, who was his brother's fund-raising chief, about Burris raising money for the then-governor.

A likely line of inquiry at this point would be to square testimony from Durbin and Reid with statements Burris has made.

A Sangamon County investigation is also ongoing over whether Burris perjured himself before the state House's Blagojevich impeachment panel.

Burris spokesman Jim O'Connor said the "policy of this office is not to discuss details of an ongoing investigation."

The Senate Ethics Committee does not comment on probes.