"Seung-Hui troubled his parents when he was young because he wouldn't talk, but he was well-behaved. I don't know how I can compensate for the responsibility for raising my kids improperly," Mr Kim told the Dong-A Ilbo newspaper.
Kim's sister said she remembered Seung-Hui as a quiet child.
"He was a good-looking boy but he wouldn't talk. If I nudged him and tried to talk with him, he wouldn't answer," Kim Yang-soon, 84, told Reuters Television.
The apartment owner says Cho's father told him it would be better to live in "a place where he is unknown."
The gunman's family lived in an off-white, two-story townhouse in Centreville.
"He was very quiet, always by himself," neighbor Abdul Shash said of the gunman.
Shash said the gunman spent a lot of his free time playing basketball, and wouldn't respond if someone greeted him. He described the family as quiet
But she said friends of hers who went to middle school with Cho told her they recalled him getting picked on there.
"There were just some people who were really mean to him and they would push him down and laugh at him," Roberts said Wednesday. "He didn't speak English really well and they would really make fun of him."