In Snowpiercer (2013), why were Namgoong and his daughter in prison? Was it because they were "drug addicts"?
The sticker on his prison locker states that he's a Kronol Addict.
"Namgoong Minsu. Kronol addict."
While this might be acceptable behaviour for the dilettantes found at the front of the train, Namgoong and his apprentice (his daughter) are engineers who would, presumably be expected to remain clean and sober in order to do their jobs.