Illinois State Police have launched a criminal investigation at the Tamms Correctional Center after leaks to reporters about the process of closing the prison.

Spokeswoman Monique Bond says "there is an ongoing investigation into criminal activity." She would not say more.

But an employee at Tamms says investigators attempted to interview nine workers there Tuesday. Most of them did not agree to answer questions.

Three investigators were from the state police and one from the Corrections Department, said the employee. He would speak only on condition of anonymity for fear of retaliation.

The prison agency has been concerned about confidential information leaking to the news media about Tamms, which is scheduled to close at month's end.