A Chicago man has pleaded guilty to four federal charges and admitted making bomb threats in his “war on SIU,” prosecutors said Thursday.

Derrick Dawon Burns, 22, admitted sending four letters threatening Southern Illinois University at Carbondale, students, staff, campus police and the FBI between Oct. 10, 2012 and Oct. 1, 2013, prosecutors said.

Three letters were titled “The War on SIU,” authorities said. One was placed in a mail collection box on campus and the others were discovered in mail sorting machines in the area, his plea says.

The original charging documents say Burns threatened to blow up buildings and rape and decapitate female students, among other threats. One letter prompted the university to evacuate three dorms.

Another said, “Give me $50 million or SIU is history,” court documents say.

After a psychiatric exam, Burns was found competent to stand trial. Burns’ lawyer, Thomas Keefe III, declined to comment and said he could not provide any reason why the letters were sent.

In a statement announcing the plea, prosecutors also provided no reason.

Burns pleaded guilty Wednesday to four counts of willfully making a bomb threat and could face two years or less in prison under federal sentencing guidelines at a Dec. 8 hearing.

Robert Patrick can be reached at 314-621-5154, @rxpatrick on Twitter or [email protected].