– For years after the 9/11 attacks, Americans worried about fundamentalist Islamic cells infiltrating the homeland and radical jihadists hiding in their midst.

The latest mass shooting at a U.S. military base — and the second in five years at Fort Hood, Texas — raises a potentially more disturbing question: Have the Iraq and Afghanistan wars created American-grown human time bombs with grievous mental and physical wounds that the military and veterans' health care systems can't adequately track and treat?

Senior Army officials Thursday provided conflicting views of Specialist Ivan Lopez's state of mind before his shooting rampage at Fort Hood a day earlier. Lopez killed three people and wounded 16 others before taking his own life.

Lt. Gen. Mark Milley, the commander at Fort Hood, said Friday that Lopez's mental health was "the fundamental underlying causal factor" in the shooting. He said Lopez had an argument with colleagues before opening fire.

Not a threat to others

But Army Secretary John McHugh told Congress that a psychiatrist's examination of the Puerto Rico-born Lopez in March had not disclosed deep enough problems for him to be viewed a threat to others.

"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," McHugh told a Senate committee.

Lopez, who served four months in Iraq, was being treated for depression, anxiety and sleep disturbance, McHugh said.

Relatives of Lopez said he had told them that he had sustained a brain injury and was suffering from post-traumatic stress disorder.

Whatever Lopez's condition or motive turns out to be — should it become known at all — his rampage brings to at least nine the number of fatal criminal shooting incidents at U.S. military bases since 2008. It was the same year that the number of American troops in Iraq peaked and the United States was fighting another war in Afghanistan.

Previous tragic incidents

In November 2009 at Fort Hood, Maj. Nidal Hasan killed 13 people and wounded 32 more. Aaron Alexis, a former sailor, shot 12 people dead last August at the Washington Navy Yard.

With the suicide rate rising among both active-duty service members and veterans, analysts said the military and veterans' health care systems are struggling to deal with mental health problems exacerbated by 12 years of war.

Drake Logan, a researcher with Civilian-Soldier Alliance, a group that tries to give service members a greater voice, said commanders often ignore the directions of mental health providers treating their troops.

"Commanders in the military are allowed discretion over soldiers' medical and mental health treatment and the work restrictions that are placed on them by medical professionals," Logan said.