Prosecutors said a DeKalb man charged in the death of a slain Northern Illinois University student told police the teenager died of a seizure.

Prosecutors revealed 36-year-old William Curl’s story during a pre-trial hearing Tuesday. Curl is charged in the death of Antinette “Toni” Keller.

This was the first time authorities have detailed what Curl told them about Keller’s death.

According to the Chicago Sun-Times, prosecutors said at first Curl refused to say anything, but then told them he found Keller dead in a DeKalb park. According to the article, Phil Montgomery, DeKalb county assistant state’s attorney, said Curl told prosecutors he panicked and burned Keller’s body when he tried to move her and some of her blood stained his clothes and shoes.

Montgomery said Curl later told investigators Keller died during a drug-fueled sexual encounter. According to the Chicago Sun-Times, Curl told investigators he found Keller taking the drug Ectasy in the park and had consensual sex with her, during which she suddenly died.

Keller was an 18-year-old art student from Plainfield. She was last seen Oct. 14, 2010, when friends said she went to a park near NIU. Her burned remains were found two days later.

Curl is set to go to trial on June 11 on charges of first-degree murder, criminal sexual assault and arson.