Five lawyers familiar with the investigation tell the newspaper that authorities also are trying to find out if money was passed from Bernard Kilpatrick to his son. The lawyers asked not be identified.
They say the former Wayne County commissioner is under investigation as part of a $47 million sludge recycling deal and contracts for work at Detroit's Cobo Hall.
The Associated Press left messages after hours Friday seeking comment from his attorney, Abraham Singer. Mayoral spokeswoman Denise Tolliver tells the Free Press "that the mayor hasn't taken any payoffs."
Kwame Kilpatrick is facing 10 felonies in two separate trials in Wayne County Circuit Court.