@Pyoro the first chapter implies that registering yourself as a Border will get you back some rights (and presumably responsibilities), the issue in this chapter is that Reika isn't registered. She isn't legally recognised at all, a non-entity.
If she were to commit a crime, the police would arrest her, find out she's a Border, get her declared dead, send her to the morgue and work from there. Presumably they'd register her and re-apply any charges as if she was registered at the time.
The alternative being that they process her as a dead body and any punishment would fall under the auspice of 'tending to a corpse' - Store the body for a while in a locked cabinet, perform an autopsy, perhaps even cremate the body. The official report would be that the perpetrator died when being arrested. If they're lucky, they'll get out and get registered.
You can see why Borders wouldn't want to risk 'slipping under the radar'.