what really happened on 9/11?

I have seen a couple of videos and read some articles from "conpiracy theorists" who have all kinds of opinions of what happened and how it happened. But not too long ago I saw this one called "loose change", and i gotta say that those guys questions are pretty straight forward and serious, and something is happening behind the veils. How come that the mainstream media is not making sure this is not true? or the government itself? why is there no serious and objective investigation going on to discredit such claims? could it be true, that our leaders, the ones that are supposed to guide us and protects us, are playing with our lives for the sole purpose of greed? could that really be?