Yongfei Ci, 29, is accused of fatally stabbing Mengchen Huang, 25, at her apartment in Urbana Friday morning, the Chicago Tribune reported.
Huang was also a student at UI.
The coroner has ruled her death a homicide.
Police went to the apartment after the dead woman's roommate said a former boyfriend had killed Huang.
The roommate said the man forced his way into the apartment and held the women captive. The intruder forced the roommate into the bathroom. She fled the apartment after the man left.
Police identified Ci as the suspect. He called police and said he would surrender. Police arrested him at a motel.
Ci, a Chinese citizen, is a sixth-year doctoral student in mathematics, the University of Illinois math department website said.
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