It's easy to point to signs of mental illness in the accused Arizona gunman. What's harder to pin down is whether health, legal or education systems should have prevented his bloody rampage.
Jared Loughner was a troubled 22-year-old who scared his classmates and instructors at a community college, posted incoherent, conspiratorial ramblings on the Internet, and drove his friends away.
Prosecutors say Loughner attempted to assassinate US congresswoman Gabrielle Giffords, shooting her in the head from point-blank range as she met constituents on Saturday at a routine meet-and-greet outside a supermarket.
Giffords and 13 others were wounded, and six others, including a nine-year-old girl and a federal judge, were killed as the gunman sprayed bullets from his semi-automatic Glock pistol.
Experts say that while the public's desire to apportion blame for such a disaster is natural, it is difficult to foresee the use of deadly force by a mentally unstable individual.
"Everyone wants to hold someone accountable when an egregious thing such as this has taken place, (but) I think these kinds of episodes are terribly hard to predict," Scott Miller, a psychotherapy expert and founder of the International Center for Clinical Excellence, told AFP.
"In retrospect, it's easy to reconstruct the path that led to this, but the causes remain elusive."
Loughner was kicked out of Pima Community College after several run-ins with campus police and could only come back if a mental health professional assured he would not be a threat to himself or others. He did not return.
But the extent to which a school should notify parents and insist on medical evaluations in such cases, especially when the subject is an adult, remains a matter of debate.
A similar controversy swirled in the United States after the 2007 massacre at Virginia Tech, where troubled student Cho Seung-Hui murdered 32 classmates and teachers in the worst school shooting in US history.
On Tuesday Loughner's parents broke their silence to apologize to victims and their families and express shock at their son's act of barbarism, saying in a statement: "We don't understand why this happened.
It remains unclear whether the college spoke directly with Loughner's mother and father about their son, and whether the parents were even aware of his steadily deteriorating condition.
"We want it to be simple but it's not," said professor Lisa Dixon, who heads health services research at the University of Maryland School of Medicine.
It appears "there were signs that weren't necessarily missed," she added.
Ken Duckworth, an assistant professor at Harvard Medical School, said some health centers have their hands tied by school policies that enshrine the right to privacy.
That could leave many students vulnerable just as they enter the amorphous middle ground between adolescence and adulthood when, experts say, a person is most likely to start exhibiting characteristics of schizophrenia.
"Typically, there's all this concern for people's privacy," Duckworth said, pointing out that when an American turns 18, he can "shut his parents out of the equation."
As medical advances have allowed more mentally vulnerable people to attend college, schools have grown more reflective of society and its demons, further taxing an already overstressed system, Duckworth said.
Substance abuse also peaks at this age, and experts say the most at-risk mentally ill people are those who use and abuse drugs and alcohol. Throw in easy access to guns through relaxed laws, and the combination can be toxic.
"You can go to Walmart and get ammunition more easily than getting a mental evaluation" in Arizona, Duckworth said.
Experts agree that the level of violence among the mentally ill is low.
But Michael Fitzpatrick, executive director of the National Alliance on Mental Illness (NAMI), minced no words in blaming a failing mental health system that may have contributed to the suspect's deadly outburst.
"Nationwide, the mental health care system is broken. Arizona, like other states, has deeply cut mental health services," he said in a statement.
Miller, the psychotherapy expert, said such rampages as Tucson's remind him of the uphill battle experts face in a health system "strained to the breaking point."
"The challenge is not separating us as a society from the person who did this deed," Miller said. "He's one of us. We have to look at ourselves."
Explore further: What's new in autism spectrum disorder? Harvard Review of Psychiatry presents research update