Possession seems to be a very nebulous concept in English and US law (probably because of their common law systems).
In contrast, German law defines possession as "having effective control" (with some more nuance obviously). Possession is also entirely different from ownership in German law. I can not control an object I have no knowledge of. If you place an object in my house, I only gain possession of it once I discover it.
I think this is one of the cases where the civil law approach of rigorous definitions is clearly superior to the common law approach of establishing precedent.
Possession of narcotics is a crime, isn't it?