Maybe the guy was just doing an oil change on his old car, and dropped the oil container at some point, and just ran because he was afraid he was going to get billed for the cleanup?
Just a thought...
That is impossible, it's a two story building and the oil was wall to wall on every steps and he also carefully put oil on another section of stairway leading to the appartements in the basement. And when my neighbor arrived from the basement (doing laundery) she saw him pouring it then run away quickly.
Actually the police thought it's a mix, like there was another substance mixed in the oil.
Thanks for the suggestion about a Simplex style lock, I'll suggest it to the owner and my neighbors.
Frankie