ROCK ISLAND -- An Illinois prison inmate has pleaded guilty to threatening to kill prosecutors and judges in three Illinois counties.

The. U.S. Department of Justice says Lewis L. Clark pleaded guilty Thursday in federal court to four counts of mailing threatening communications.

Clark sent letters in December 2008 and January 2009 while he was imprisoned at the Pontiac Correctional Center. The letters went to judges and prosecutors in Henry County in northwest Illinois, Adams County in western Illinois and Vermilion County on the Indiana state line.

The Justice Department says Clark will be sentenced Jan. 28. He faces up to five years in prison on each count.