Dan1113 wrote:
Workers who have made mistakes doing maintenance have gotten long jail terms.

This wasn't really what I would call a mistake, they knew it should be on and they deliberately had it off. Of course they figured nothing would happen but it did. They didn't have it off by accident. If you murder someone by a mistake, you'll still be prosecuted even if you didn't mean killing that person... and this was waaay beyond that.
If I neglect to turn on the headlights on my car one night and someone smacks into me and dies as a result, I don't think I'd stand criminal charges beyond a traffic ticket for my actions unless I was illegally under the influence of drugs or alcohol. Now, I'd be civilly liable and probably have the pants sued off me, but that's another issue altogether.