Joseph D. Konopka, 29, pleaded guilty to 11 felonies Friday in federal court in Milwaukee. The most serious charges carry mandatory prison terms of five to 20 years.

Konopka, a former computer systems administrator who went by the online name "Dr. Chaos," already received a 13-year sentence in Chicago, where he was convicted of two felonies for hiding cyanide in a tunnel near the subway system.

At his Oct. 25 sentencing hearing in Milwaukee, his attorney, Bridget Boyle-Saxton, can argue he should receive a concurrent sentence to his 13-year term.