In 1992, determined to find a better life, the Cho family immigrated to the United States, settling in Washington, D.C.'s large, thriving Korean community.
Cho's parents both worked long hours in the dry cleaning business. Cho attended Poplar Tree Elementary School in Chantilly, Va. He was 9 years old, and didn't speak much English, but it soon became clear he wouldn't speak at all.
It was at Poplar Tree Elementary that Cho was first identified as having developmental problems -- both emotional and verbal. The school put him in an individualized education program, or what might be called special education. The school also offered the family outside counseling.
Dr. Bela Sood, a member of the official Virginia Tech review panel, spoke with Cho's family. In an exclusive interview, Sood told "Nightline" that Cho, "did appear very withdrawn and quiet, and the school was very quick at picking that up."
A veteran child psychiatrist, Sood said Cho got a lot of help, both from school officials and from his hard-strapped immigrant family. A family acquaintance, who agreed to an interview with "Nightline" on the condition that her name wasn't used, remembers the family's struggles with their son.
"When he first came to America he was in about the second grade," said the acquaintance. "Every time he came home from school he would cry and throw tantrums saying he never wanted to return to school."
Throughout these school years, Cho's classmates recognized him as different. According to Patrick Song, a classmate of Cho's at both high school and Virginia Tech, "He just had this demeanor about him where he would just walk around, and he would always face down. He would never look anyone in the face really, his eyes were always down, his shoulders down. He kind of had a puzzled, confused look on his face, but it was serious. It was really depressing to look at him."
Ben Baldwin went to middle school, high school and Virginia Tech with Cho. "The teacher would call on him to read a passage from like a story or like a play in English class and he would just sit there and he wouldn't talk, or if he would, he would mumble and then the teacher -- if he wouldn't talk -- the teacher would actually physically come up to him and like prompt him, like, 'Hey, do this for me. Come on just read this passage Seung and we can move on."
And then, in 1999, Columbine shocked the nation. Cho was in the eighth grade. The 15-year old was transfixed by the horror, and his teachers noticed that menacing, dark and violent fantasies erupted in his school work.
"I remember sitting in Spanish class with him, right next to him, and there being something written on his binder to the effect of, you know, '"F"' you all, I hope you all burn in hell,' which I would assume meant us, the students," Baldwin said. "And the teacher saw that and she came over and she got him, talked to him for a little bit … and then took him out of the classroom."
According to Sood, "It appeared as though the Columbine shooting set off in his mind the fantasies around suicide and homicide which were picked up in a class essay…and was picked up by the teacher who then sought the parents out and suggested that he be evaluated and which led to the psychiatric evaluation and the intensification of the counseling."