The test results were submitted as evidence during a hearing Thursday for William Curl.
He was arrested after Antinette Keller, 18, of Plainfield, vanished.
In October, the NIU freshman disappeared after telling friends she was taking a walk in a nearby park.
Her burned remains were found two days later, but investigators had to wait for test results to confirm the body was hers. Prosecutors said DNA was taken from Keller's parents to compare with DNA from Keller to confirm the remains were hers. Police found Keller's burned clothing and her cell phone near the remains.
Curl is charged with first-degree murder, criminal sexual assault and arson in Keller's death.
Investigators said it appears to have been a crime of opportunity and that Curl did not know Keller.
The Associated Press contributed to this report.