Before the "Well they're just fictional images, so what's the harm?" brigade shows up (hopefully we left them on Reddit), he was using photographs of real children. People would send him photos of children they knew in their personal lives who they wanted to see in sexual abuse situations and he would create the images. He was also convicted of encouraging the men he was talking to to rape children in real life.
Because I wasn't sure, the way your comment comes out swinging.
Too many threads like this feature people who are convinced that corporate models were trained on hyper-illegal pornography (with accurate human labeling!) or that the absence of real human persons is no excuse. Like they're not clear why this specific thing is as illegal as possible.