A 17-year-old boy who sexually assaulted a pregnant college student and locked her in the trunk of a car has been charged as an adult with aggravated criminal sexual assault, a state's attorney said.

The teenager was ordered held without bond Sunday after police arrested him Friday. He is also charged with aggravated kidnapping and armed robbery of the 24-year-old Chicago State University student.

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The Associated Press generally doesn't name juveniles accused of crimes.

The woman was gathering books from her car near campus Wednesday afternoon when the teen held a steak knife to her side and forced her to drive to an alley, Assistant State's Attorney Elizabeth Novy said. The woman told the teen she was pregnant and showed him her belly, she told police. He then sexually assaulted her, stole $160 and locker her in the trunk, Novy said.

The woman escaped from the trunk using an interior release. Investigators found the teen's fingerprints on the car and he later admitted to what happened in a written statement, Novy said. He was on electronic monitoring for attempting a similar attack in July, she said.

The university issued a community safety alert and is cooperating with investigators, police said.