Questions:
How are the doors powered? Are they automatic, basic wooden, panel doors?
Does the glass door function differently to the other doors?
Have you ever been on an AMTRAK train? Seriously people, look it up. It's awesome in California. :3
But in all seriousness, for the sake of simplicity, the story is set in modern times (i.e. - now), meaning that instead of wooden doors, all doors reflect the construction of the train itself. Remember that sentence about "...polished steel ceilings and walls"? Apply that to the doors. (Also, yes, they're 'automated' in the sense of you pushing a button, waiting a few seconds for it to fully open, and then going through, but can be forced open with one's hands).
The glass door is just like any door, with the exception that you can see through it from both sides (all other doors connecting the carts together or the doors that allow exit/entrance to the train only have a small window to see through). Otherwise, it's slightly more fragile (because it's glass, not metal or wood), and requires a more...
delicate operation to lock/unlock/open/close it.
...Let's take some very wild swipes in the darkness.
The shadowy figure (the one I saw in the fog before I boarded the train) is the warlock.
I glimpsed the shadowy figure at the back of the train before I boarded it.
The shadowy figure supplied the crowbar to Ivan, allowing him to get onto the roof, in exchange for a favour of delivering poison onto Zack's food.
Jack used the glass door to enter the lower floor to enter the engine room after Ivan had entered and left the engine room. Jack stopped the train from the engine room.
OR
I glimpsed the shadowy figure at the front of the train before I boarded it.
The shadowy figure entered the cockpit and killed the pilots.
Jack entered this room, was shocked by the corpses, shut down the train and hid in the cockpit.
OR
The shadowy figure then proceeded to hide in the cockpit.
Ignoring the very first statement (figure = warlock) because that doesn't solve anything.
The shadowy figure did not supply anything to anyone.
Jack never used the glass door.
The shadowy figure was not at the front of the train, because a driver would see that and would prevent the train from leaving.
The shadowy figure never entered the cockpit/driver's cart.
Jack could not shut down a train as he had no license to pilot the train.
The last sentence is defeated by the 2nd-to-last black truth (what exactly do you mean by cockpit though? Like, a special driver's section or something?).
