The main gate at the Fort Hood Army Base is seen on South Fort Hood Street in Killeen, Texas on November 7, 2009. Maj. Nidal Malik Hasan is charged with the deaths of 13 and 29 others wounded after a shooting spree at the Fort Hood army base on November 5. UPI/Robert Hughes | License Photo

KILLEEN, Texas, April 5 (UPI) -- Witnesses said U.S. Army Spc. Ivan A. Lopez was involved in an argument about paperwork just prior to opening fire on soldiers at Fort Hood in Texas, killing four people.

Lopez was apparently involved in a spontaneous argument over paperwork Wednesday in a human resources office.


The witnesses said the military truck driver asked for a leave-of-absence application but was told to return for it the next day. He became exasperated during the incident.

Lopez left and returned moments later with a .45-caliber Smith & Wesson semiautomatic pistol and opened fire on members of his unit, the 49th Transportation Battalion, the Washington Post reported. He killed two people.

He then left the building and began shooting at other soldiers, eventually killing one other person.

He tried to leave the base in his vehicle but was confronted by a military police officer in a parking lot. Lopez then shot himself in the head, taking his own life.

Still, investigators said they don't know the reason for Lopez's actions.

“We have not established a concrete motive, but we will do everything in our power to do so,” Christopher P. Grey, a spokesman for the Army Criminal Investigation Command, said at a news conference at Fort Hood. “Given that the alleged shooter is deceased, the possibility does exist that we may never know exactly why the alleged shooter did what he did.”