Can someone explain to me

It's purposefully left ambigious what was in the suitcase. The point is the suitcase is mysterious and makes people want to know what's inside it, which then leads to their death.


If you want a really shitty theory about it though, my first thought was it was some sort of supernatural predator which disguised itself as a mundane item so it could capture more prey. I think it was something like the monster in Detective's Assistant except it had the ability to lure prey to it, sort of like an anglerfish.

that makes sense