Karl Rove's decision to resign back in August came as a surprise to many. Now we may know at least one of the reasons, courtesy of The Hill's Susan Crabtree.

House Judiciary Committee Chairman John Conyers Jr. (D-Mich.) on Wednesday released an interview with GOP lawyer Dana Jill Simpson implicating former White House adviser Karl Rove in the prosecution and conviction of former Alabama Gov. Don Siegelman (D) on corruption charges.

In a closed-door interview with committee staff, Simpson recalled how Rob Riley, current Gov. Bob Riley's (R) son, told her about Rove's role in a plan to prosecute Siegelman if he did not back down from contesting the 2001 gubernatorial election results that handed the office to Riley.

According to the transcript, Simpson described a 2005 conversation with Rob Riley, who told her that Rove had contacted the Public Integrity Section of the Department of Justice to press for further prosecution of Siegelman. She said Rob Riley also recounted how the case would be assigned to a federal judge who "hated" Siegelman and would "hang Don Siegelman."

This is one of those stories that we knew even if all of the details had not yet been flushed out by intense reporting. The Bush White House has consistently used the Department of Justice to expand the power of the Republican Party, as evidenced thoroughly throughout the prosecutor purge investigations. The partisan prosecution of Siegelman is just one more manifistation of this broader effort.

It's not clear what, if anything, will come out of this revelation, whether Rove can be held liable for his actions -- or if he could if there was anyone who would even try to pursue the matter. To this last question, perhaps Michael Mukasey might have an answer -- and he should certainly be pressed for a clear one -- during the hearings over his nomination to head the Justice Department, which are apparently scheduled for next week.