Xue Longhu was at the peak of the Core Formation Stage. If he were to be executed openly, there should at least be some shocking crimes. Not just Fang Chengzhi, even Xue Longhu himself did not foresee that he would be sentenced to death due to such trivial crimes.
From what Fang Chengzhi heard later, the reason Xue Longhu's case was closed so quickly was that Xue Longhu did not realize the severity of the case at all, or rather, he did not even consider the incident as a 'case'.
He defended himself in the cases regarding forced transactions and group fights in the mines. But when it came to the incident with the child slaves, he admitted it quickly and signed his name, as could clearly be seen on his statement.