Such things sometimes can't be predicted. If you fall asleep because of exhaustion, you don't necessarily see it coming (it happened to me several years back, one minute I was fine and the next I blacked out). You cannot criminally persecute a person for falling asleep. Only if he did something against the law, like also being under the influence of alcohol.

> Did the supervisor actually threaten him into taking an extra-long shift?

You know very well that supervisors rarely have to threaten their subordinates in low-end jobs. I have a personal acquaintance who's a truck driver. And he was explaining to me how when the new management came in, they first did some lay-offs based on silly reasons and after that nobody dared arguing.

Also do some reading on Japanese culture. Subordinates rarely question their bosses (or change jobs for that matter). It happens in many cultures. If you're from the US, then what's natural to you may not apply in other countries or cultures.

I'm not saying that blame cannot be assigned (it can clearly be, especially in the case of broken engineering designs), but seeing people here suggesting "ritual suicide"? OMG.