FORT HOOD, Texas — Despite evidence that suggests Spc. Ivan Lopez had an argument before going on a shooting rampage, investigators said they may never determine what compelled the Fort Hood soldier to kill three soldiers and wound 16 others before taking his own life.

Lt. Gen. Mark Milley, Fort Hood’s commander, said an “escalating argument” precipitated the assault. He declined to discuss the cause of the argument but said investigators believe Lopez made no effort to target specific soldiers — even though at least one of the soldiers shot was involved in the dispute.

Milley would not say whether those involved were among the dead or wounded, or how many shooting victims had been a part of the argument.

“There was no premeditated targeting of an individual,” he said.

However, the military has not established a “concrete motive” for Spc. Ivan Lopez’s rampage, said Chris Grey, a spokesman for the Army’s Criminal Investigation Command based in Quantico, Va.

And because Lopez is dead, he added, “the possibility does exist that we may never know why the alleged shooter did what he did.”

Three of the wounded are still hospitalized in fair condition at Scott & White Memorial Hospital in nearby Temple.

Investigators now believe Lopez’s mental condition was not the “direct precipitating factor” in the shooting, Milley said Friday, one day after he said that condition appeared to be an underlying factor in the attack.

The crime scene encompasses two city blocks, Grey said.

Lopez initially began firing near an intersection, then traveled to several nearby buildings, went inside and kept firing.