The soldier who killed three people at Fort Hood last week fired at least 35 rounds during an eight minute rampage before turning his weapon on himself, Army investigators said Monday.
Chris Grey, spokesman for the Army's criminal investigation division that is heading the probe, said the violence followed a verbal altercation over a request for leave by the gunman, Spc. Ivan Lopez, 34.
Grey did not say whether the leave had been granted and said the shooter's motive was unclear.
"We have not confirmed a definitive motive,'' he said.
Army officials said 11 of the 16 injured have returned to duty and five remain hospitalized.
A Lopez family spokesman said last week that he was upset he was granted only a 24-hour leave to attend his mother's funeral last November, the Associated Press reported. The leave was extended to two days, it said.
At a press briefing at the base in Texas, Grey said that Lopez killed himself with a .45-caliber pistol after a female military police officer fired once at Lopez without hitting him.
According to Grey's account, Lopez fired first in the building where the argument began, killing one soldier and wounding 10 others. Among the dead was one of the men Lopez had argued with, he said.
He returned to his private vehicle and drove to the motor pool building where he was assigned, shooting and killing another person. From there, he drove to a medical building a block away, walked inside and killed a soldier behind his desk, Grey said.
"We do not know why he entered that building, and we may never know,'' Grey said.
He said Lopez fired and wounded soldiers from his vehicle while traveling between the buildings. The soldier's last stop was outside another base building where he was confronted and fired upon by a female military police officer, he said.
"This entire scenario... lasted approximately eight minutes,'' Grey said.
Investigators recovered 35 spent shell casings, including three inside Lopez's vehicle, and believe he fired at least that many times, he said.
President Obama is to attend a memorial service Wednesday at Fort Hood, where 13 people died in a 2009 shooting attack by an Army psychiatrist, Nidal Hasan, who was later convicted of the killings.