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Seung-Hui Cho and sister, Sun-Kyung Cho, were members of the "1.5 generation" -- young people born in another nation who must adapt to a new country's culture.

Conflict with parents often rears as children rebel against tradition. Parents, in the immigrant tradition, often labor long hours, creating more distance from offspring, said Josephine Kim, an expert about stresses affecting Korean immigrants.

Like Cho, Kim came to the U.S. when she was 8. She ultimately earned a doctorate in counselor education from the University of Virginia and is now a lecturer for the Harvard Graduate School of Education.

Kim said young Korean-Americans can be vulnerable to depression. But Korean cultural norms can restrain reaching out.

"Many Koreans think that mental health problems bring shame on the family and that seeking help is a sign of weakness," she said. "Some venture to think that it is a sign of bad blood or sin. They also believe that problems should stay within the family."

Kim suspects Cho was an "internalizer," someone suffering silently with psychological problems instead of acting them out in disruptive behaviors.

"Children and adolescents who internalize are those who are prone to depression, anxiety and social withdrawal," said Kim. "They're not overtly aggressive or disruptive, and because they stay under the radar, they are rarely noticed."

Jack Presbury, a psychology professor at James Madison University, said an Asian student told him that his culture "teaches that you should endure," denying feelings and psychological injuries.

"Caught between two cultures -- one that says 'suck it up' and another that says 'express yourself' -- must have been confusing for Cho," said Presbury.

If Cho had been a behavioral problem in school, said Kim, "he would have been identified to be needing services a long time ago."

Korean-American youths often shoulder additional stress, she said.

"Education is viewed as the only way to climb the social ladder in Korea. Educational success is highly esteemed while other forms of accomplishments are often deemed as futile. A filial child must sacrifice his or her desires for the greater good of the family."

It seems Sun-Kyung Cho, unlike her brother, adapted well to pressures facing the 1.5 generation. In 2000, she entered Princeton University, where she was an economics major and occasional contributor to The Daily Princetonian. She graduated from Princeton in 2004.

She last worked as a contractor with the U.S. Department of State and is listed in the department's phone directory. But the department is not her employer.

"The State Department does not have a direct employee by that name," said Leslie Phillips, a spokeswoman for the department.