Government Version:

The story changed four times. The first version was a rocket attack, next it was a mortar, next was suicide truck and the final version was a suicide bomber with a waist belt did this.

Gen Myers said, the bomber was dressed in a military uniform.
 

The bomb was placed inside the mess hall by someone connected to the food service company, or it's suppliers. A probable scenario is a Sayanim, employed by the  UK contractor, placed an Iraqi in a position where he was able to smuggle a bomb in.

The bomb was in a propane tank that used to keep the buffet tables hot.

The injuries were due to ball bearings which rule out rockets, mortar, truck bombs, etc.

The terrorist drove a van past the tent, and filmed the explosion  in detail.  The van did a remote detonation, coordinating the filming with a 5 second driving window. This would require a surveillance van, with electronic and video capabilities, and a four man crew.

 The bomb was sophisticated, and the target was psychological, which points to the Mossad.
 

Why ?

Israel goes to great lengths to portray the Arabs as monsters, and increase our retaliations. Israel has us do their killing, and they get the Iraq oil.

Israelis/Jews are buying up property around Mosul for their soon to be controlled oil fields.

The Iraqi Mossad is headquartered out of Kirkut, near Mosul.