UPDATE: Illinois State Treasurer Dan Rutherford tweeted the following Sunday evening:
PONTIAC - Sources are saying GOP gubernatorial candidate Dan Rutherford will be announcing former candidate for attorney general Steve Kim as his running mate later this week. The two names most often connected to Rutherford have been retiring State Rep. Kay Hatcher (R-Yorkville) and Kim. It is believed Rutherford wanted DuPage GOP Chair Darlene Ruscitti, but she declined.
The candidates will begin circulating petitions as soon as Tuesday, and each must have their lieutenant governor pick on the petition. Rutherford has said he'll announce his LG pick via Twitter on September 5th, then on Facebook and with a press announcement later in the day.
If it happens to be Kim, here's a video he made in 2010 when running for Attorney General: