UPDATE, 3:22 p.m.: Fort Hood officials positively identified the shooter as Spc. Ivan Lopez.
Lt. Gen Mark Milley, Fort Hood and III Corps commander, said there was a "strong possibility" the shooting may have been triggered by a verbal argument between Lopez and another soldier or soldiers.
Milley also said Lopez purchased the gun used in the shooting at Guns Galore in Killeen.
More information is coming to light about the man who killed three and injured 16 before turning the gun on himself in a deadly shooting at Fort Hood on Wednesday.
During testimony to the Senate Armed Services Committee this morning, Secretary of the Army John McHugh said the shooter, widely identified as 34-year-old Spc. Ivan Lopez, was undergoing treatment for several mental heath conditions, including anxiety and depression.
McHugh said the shooter, a native of Puerto Rico, was prescribed a number of medications as part of his treatment.
"He was seen just last month by a psychiatrist, " McHugh told committee members. "He was fully examined. And as of this morning, we had no indication on the record of that examination that there was any sign of likely violence, either to himself or to others, no suicidal ideation."
Lopez joined the Army in June 2008 as an infantry soldier. He later became a truck driver after re-enlisting. According to Thursday's testimony, Lopez lived off post, and committed the shooting with a gun purchased off post. The weapon was not registered with Fort Hood.
Read more in Friday's Killeen Daily Herald.