The Unsolvable Dungeon
Although technology in District 008 was fairly advanced, players and their bizarre items could exploit loopholes in that technology. This created an awkward situation: ordinary crimes committed by ordinary people sometimes required no human effort at all. Various instruments and armed robots could handle the entire process, from gathering evidence and identifying suspects to making arrests and securing convictions. But crimes committed by players became far more "mysterious" due to all sorts of outside factors. In many cases, it was impossible even to determine when the crime had taken place.
Among the famous cases in District 008's past was a mass crime resembling a cult ritual. The process was bloody, and the victims had died horrific deaths. The incident wasn't discovered until a week later. Every member of a small religious group that had been popular in District 008 at the time had been killed; not a single one had escaped. Yet after the investigation, no trace of any perpetrator had been found. It was as if they had suddenly decided to come from an outer district, kill everyone in the group, and then leave calmly. There had been no lead-up and no aftermath.
So, aside from a few people who weren't quite right in the head, it was simply too easy for players to conceal their motives for committing crimes. Of course, every action left some trace. The killer, whose identity was suspected to be that of an Artificer, had deliberately broadened the pool of targets, giving the city government multiple overlapping groups of people to investigate. This only showed that he knew these people's movements inside out. Since so many places were involved, some also speculated that the killer might work for the government—and hold a fairly high position.
But that theory was quickly debunked.