First, people are more idle in autumn.
Ancient people generally engaged in agricultural production, and the busiest season was spring and summer. At this time, the work in the sky and underground can't be finished, and they have no time to do anything else. When interrogating prisoners and beheading them, there are often many people watching. If you arrange to interrogate beheaded prisoners during busy farming hours, few people may have time to watch. The purpose of punishing prisoners is not only to punish themselves, but also to educate the people. Therefore, we should choose when the people are free. Autumn is a good time. At this time, the autumn harvest was basically completed, and the people had nothing to do, just to let the people see for themselves how the court handled the prisoners.
Second, the ancients were superstitious.
Ancient people didn't understand science and were superstitious about nature. When they see autumn, everything is bleak and the leaves fall back to their roots. At this time, killing prisoners is more in line with the characteristics of this season. In spring and summer, plants are full of vitality, and it is not in line with destiny to deprive people of their lives at this time. Therefore, the ancient government decided to ask about autumn logging.
Apart from these two reasons, I personally think it is still colder than the weather after autumn. At this time, prisoners are not so easy to rot and spread diseases, so choose to ask after autumn.