A dispute over paperwork could be the reason behind the shooting spree that left three people dead and more than a dozen injured at Fort Hood in Texas.  

Several sources say that Ivan Lopez had been denied a leave of absence form earlier that day.  

Speaking at the Army installation Friday, investigator Christopher Grey said Lopez had the argument, opened fire on several soldiers, and then killed himself when he was confronted by a member of the military police.

He said they're still looking for a concrete motive in the case.