WASHINGTON -- 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 less than 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 Spec. Ivan A. Lopez's state of mind before his shooting rampage at Fort Hood a day earlier. Lopez killed three people at the base and wounded 16 others before taking his own life.
Military officials said that Lopez bought the gun he used in Wednesday's attack on March 1, but had not registered it at Fort Hood as required by regulations.
"We have very strong evidence that he had a medical history that indicates an unstable psychiatric or psychological condition," said Lt. Gen. Mark Milley, the commander at Fort Hood. "We believe that is the fundamental underlying causal factor here."
Army Secretary John McHugh, however, told Congress that a psychiatrist's examination of the Puerto Rico-born Lopez last month had not disclosed deep enough problems for him to be considered 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 the Senate Armed Services Committee.
Lopez, who served four months in Iraq, "was undergoing a variety of treatment and diagnoses for mental health conditions, ranging from depression to anxiety to some sleep disturbance," McHugh said. Lopez had been "prescribed a number of drugs," among them Ambien, a common sleeping pill, McHugh said.
Relatives of Lopez said he told them that he had sustained a brain injury and was suffering from post-traumatic stress disorder, or PTSD. The Pentagon did not confirm those health problems.
Whatever Lopez's condition or motive turns out to be -- should it become known at all -- his rampage Wednesday 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 reached a peak and the United States was simultaneously fighting another bloody war in Afghanistan.
In November 2009 at Fort Hood, Maj. Nidal Malik Hasan killed 13 people and wounded 32 others. Hasan, a self-avowed jihadist and "soldier of Allah," was sentenced to death last year and is imprisoned at Fort Leavenworth, Kan.
Aaron Alexis, a former Navy sailor, shot 12 people dead last August at the Washington Navy Yard before he was slain.
With the suicide rate rising in recent years among both active-duty service members and veterans, analysts said the military and veterans' health-care systems are struggling to deal with a broad range of mental health problems exacerbated by more than 12 years of war.
Drake Logan, a researcher with Civilian-Soldier Alliance, a group that tries to give service members a greater voice, is completing a report based in part on extensive interviews over the last two years with soldiers at Fort Hood and veterans who formerly served there.
Logan said commanders at Fort Hood and other military installations where she's interviewed service members often ignore or countermand 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.
Harry Croft, a former Army psychiatrist who has treated 1,700 cases of PTSD and wrote a 2012 book on the illness, said he and other health-care providers tread a thin line between trying not to exaggerate such problems and imploring the government to do more to address them.
Noting that Lopez was under treatment when he went on his rampage, Croft said it is very difficult to identify such insider threats in advance.
"We still can't predict with tremendous accuracy whether someone is going to go out and hurt themselves or other people," Croft said. "I wish we could, but it's as much an art as a science."
Sen. John Cornyn, a Texas Republican, made a similar point at a Fort Hood news briefing with Milley.
"Mental health issues are the most vexing issues from my perspective in terms of how do we identify people who have genuine problems that need to be treated," Cornyn said. "But I think at the same time, we have to be very careful and not paint with too broad a brush and assume that just because someone has been in combat that they necessarily have those issues."
In releasing the results of Pentagon investigations probes of the Washington Navy Yard shootings, Defense Secretary Chuck Hagel last month said that the reviews had "identified troubling gaps in our ability to detect, prevent and respond to instances where someone working with us -- a government employee, member of our military or a contractor -- decides to inflict harm."
Almost one-third of all Iraq and Afghanistan veterans seen at Department of Veterans Affairs medical facilities have been treated for PTSD, according to the most recent VA report, and mental disorders are the second most frequent diagnosis.
While veterans have better luck finding jobs than their civilian counterparts, younger former troops who fought in Iraq and Afghanistan still lag behind, the Bureau of Labor Statistics reported last month.
"At the same time we recognize that the vast majority of our military and vets are not in crisis, we must all acknowledge that there are indeed problems with the way mental health and transitional support is managed and available to our service members and veterans," Paul Rieckhoff, founder of Iraq and Afghanistan Veterans of America, told a Senate panel last month.
Veterans Affairs Secretary Eric Shinseki told Congress last month that his agency added 2,400 mental health providers in the past two years, but shortages remain.
White House press secretary Jay Carney said Wednesday that President Barack Obama is frustrated by the failure of Congress to act on his legislation to increase mental health and criminal background checks for gun buyers.
"During the course of (more than) a decade of war, many (service members) have been on multiple tours of duty," Obama said. "To see unspeakable, senseless violence happen in a place where they're supposed to feel safe, home base, is tragic."