A Northern Illinois University student was arrested Tuesday after authorities said he admitted to using artificial intelligence to create deepfake child sexual abuse material of female students, most of whom he went to high school with.

“There was one from when I was 15. I’m almost 20 years old now,” one victim told Chicago station WGN-TV.

The victim’s adolescent photo was one of many images that 19-year-old Michael Erickson allegedly used to produce realistic-looking images with the help of AI, according to the outlet. Police say most of the victims had been Erickson’s classmates and were between 13 and 17 years old at the time the photos were taken.

Erickson was charged this week with 21 felony counts related to child sex abuse material, including “production of child pornography, disseminating child pornography and possession of child pornography,” according to a press release shared with HuffPost.

A lawyer listed in Erickson’s records did not immediately respond to a request for comment.