Democratic Illinois Gov. JB Pritzker, his wife and his brother-in-law are under federal criminal investigation for a dubious residential property tax appeal that dogged him during his gubernatorial campaign last year, WBEZ has learned.

A law-enforcement source familiar with the investigation confirmed to WBEZ that the probe, which has not been revealed publicly until now, began last October and remains active. There are no signs that criminal charges are imminent.

WBEZ has also confirmed that Illinois First Lady MK Pritzker’s personal assistant who was involved in the property tax appeal, Christine Lovely, is being represented by one of Chicago’s most high-powered lawyers. Her attorney, Reid Schar, is a former federal prosecutor who helped convict ex-Illinois Gov. Rod Blagojevich on corruption charges.