in case of:(In case of = in the event that, if it should happen that there is a(n) ___________).
In case of emergency, the family always kept a first aid kit in the car.
in the case of: this refers to a specific instance or topic:
In the case of the students who qualified for honors this term, no exceptions were allowed.
in possession of= having in one's possession 'Mr. Blaine is in possession of a fine collection of antique silver spoons.
in the possession of=belonging to or in the custody of:
The fine antique silver spoons are in the possession of Mr. Blaine.
I hope this is helpful,
Student or Learner