Here is the sound of a JDAM missile (it does sound exactly the same as the sound in the first video)
Here is another video (from a different angle) showing the explosion
Now there are some people who are saying that since it was a fertilizer plant there are chemicals contained within that can cause this kind of damage which is true. Read through the comments on the videos (and others on YoutTube) as many people have written about these chemicals and their volatility but some have also debunked some of these assertations.
There are also 3 other reasons that people think this might be a conspiracy:
1) There was supposed to be a "drill" taking place
2) A helicopter or plane was supposed to be in the area
3) Apparently this fertilizer company had a pending lawsuit against Monsanto
Again I am not here to say yes it was a conspiracy or no it wasn't. I just like passing along information as I love conspiracy theories and know others do also :)