I'm really not sure of what the big deal is about what is actually in the bag.
It's just papers, old newspapers and flyers and stuff, just general paper/cardboard rubbish, you can see that clearly through the somewhat transparent bag. The bag that was dumped previous to the last one had a cardboard coffee-cup at the top of it that was extremely obvious you could even see a straw poking out a little.
There is nothing spectacularly obvious that would merit a further investigation IMHO. There's no outline of human body parts, no hint of blood-stains, nothing that looks like it could be a weapon or a bomb, the bag doesn't move or make a noise so there's no abandoned kittens, puppies or babies in it. It's just papers.