Austin - Cellphone videos of Corpus Christi State School employees forcing mentally disabled residents into late-night prize fights have left Texas families and advocates for people with disabilities in search of answers - not just about security but about human nature.

How can one human being treat another in such a wicked way? Experts disagree on the roots of such abuse. It might be a byproduct of the stressful situations people are in. It could also be innate sadism.

But they concur that the formula at Texas' 13 institutions for the disabled - young, inexperienced and underpaid workers in charge of the state's most vulnerable residents - lays the groundwork for disaster.

"Left alone, human beings will engage in the most surprising kinds of misconduct and adjust their mentality to fit," said David Crump, a University of Houston Law Center professor who specializes in the psychology of evil behavior. "We should expect this unless we take concrete and meaningful steps to prevent it.

Psychologists, criminologists and ethicists have long sought to understand why some people derive pleasure from acts most consider evil, from the Holocaust to Rwandan genocide to abuse in Iraq's Abu Ghraib prison.

Some researchers believe that sadism has a genetic component, and that people who are biologically predisposed to it select jobs where they have authority over others' well-being. Barbara Oakley, a biomedical engineer and author of the book Evil Genes, said there appears to be something hardwired in the brain that prompts aggressors to "feel pleasure when they do what they do."

Many others say cruel behavior is a response to a perfect storm of conditions that have nothing to do with inherent evil.

In a notorious Stanford University experiment from the 1970s, psychologist Philip Zimbardo created a mock prison and randomly assigned students to be guards or captives for a two-week stretch. Within days, the "guards" were beating the "inmates," trapping them in dark closets for long stretches, and forcing them to simulate sex acts. The experiment got so out of control that Zimbardo had to shut it down after just six days.

The abuse, Zimbardo theorized in his book The Lucifer Effect, couldn't have been innate. The "guards" were congenial, bright students from good families, who returned to their normal selves after being released from the study.

What he found was that even good people would treat others with violence under certain high-pressure conditions. That good character would fall by the wayside when people were isolated from the outside world. And that hardly anyone would challenge the injustice before them.

Conditions were compounded whenever training was inadequate, hours were long, and work was boring, he noted. They were always worse at night, when supervision and scrutiny were lax.

Reached by e-mail Friday, Zimbardo wrote: "Good people are often seduced into behaving in evil ways by situational forces of which they are unaware - group dynamics, authority, power, anonymity and more."

By Zimbardo's account, cases like the Corpus Christi State School aren't astonishing; they're predictable. The employees accused of forcing disabled residents from their beds and provoking them to fight were young and inexperienced; none had been on the job more than two years. They worked the night shift, when supervisors and the facility superintendent were not on campus. And they made between $19,000 and $22,000 annually - less than a job at McDonald's or Wal-Mart.

Some researchers say there could've been other psychological factors at play in Corpus Christi, too. Eric Stocks, an assistant professor of psychology at UT-Tyler, said this could've been a case of "pluralistic ignorance" - where no one was comfortable with the abuse but believed everyone else was and didn't speak up.

And, he said, it shows telltale signs of "empathy burnout," where people who start out compassionate begin to dehumanize or resent those they're caring for.

Robert Roberts, distinguished professor of ethics at Baylor University, said that when these employees are poorly trained and outside of their comfort zone to begin with, they're already at risk of acting out. Roberts recalled "one horrible time" many years ago when, working as a youth minister, he struggled to get an out-of-control youth to comply.

"I actually got violent with him, twisted his arm in a way that hurt him," Roberts said, horrified even now. "When you're not adequately trained, not prepared - there's some kind of unprecedented character to a situation that makes people act in ways they normally wouldn't."