YG,
I too have heard that the briefcase contains Marcellus’ soul. One piece of evidence towards that theory is that you never see Marcellus’ face until AFTER he gets the case back, i.e. before that he is souless and hence has no face.
That’s interesting, there should be a separate movie explaining all this stuff. Do you have an explaination as to why they waited a few minutes before entering the apartment?