I figured out how to get to know Lavius' motives, I managed to proceed by doing a sanity check on Ionut after moving the box into the basement to figure out what is in it. (I'm sure I did it before but I might've forgotten to redo it again after loading a safe somewhere) You'll discover what's in the box and you learn it only comes out at night. (not sure if this is important as i never got it to be that late) after this you can play pool against Lavius once more and you'll have a new dialogue option. From that point it looked pretty straightforward in my opinion.