Door won't unlock/open

[Pavel14]

Unfortunately, the vehicle is at an isolated location, so bringing in a locksmith isn't practical (I only get to the location once a fortnight or so). Thought to attempt to find the same mechanism in a wrecking yard and study how it works. Perhaps then I can figure out a way to open the closed and locked door from the inside...

I'm wondering if there isn't some kind of spring loaded "cog" inside the lock itself - perhaps an internal spring is broken? If I had just left the door unlocked...