Cho Seung-hui left South Korea with his family in 1992 to seek a better life in the United States, Cho's grandfather told the Dong-a Ilbo daily. Cho killed himself and 32 others at Virginia Tech in the deadliest shooting rampage in U.S. history.
Relatives said they had minimal contact with the family after they left South Korea.
"How could he have done such a thing if he had any sympathy for his parents, who went all the way to another country because they couldn't make ends meet and endured hardships," Cho's maternal grandfather, identified only by his last name Kim, was quoted as saying.
The 81-year-old Kim said Cho "troubled his parents a lot when he was young because he couldn't speak well, but was well-behaved," the report said.
Kim said he had little communication with Cho's family after they left for the U.S.
Cho's uncle - his mother's younger brother - also told the newspaper that he was unaware of how Cho's family was doing.
"I don't even know my sister's phone number," the uncle said, adding he last talked to Cho's mother in October, the report said.
"Before she emigrated in 1992, she told me she was leaving for her childrens' education. Since she emigrated, I haven't seen her for nearly 15 years," the uncle - also identified by just his last name Kim - was quoted as saying.
Meanwhile, South Koreans mourned the deaths of those killed in the Virginia Tech shootings at a special church service Thursday, some fighting back tears from the guilt that a fellow South Korean was responsible for the massacre.
About 130 people gathered at Myeongdong Cathedral in central Seoul, casting their heads low as they sang sad hymns and prayed for the souls of those killed. A small table adorned with white flowers, candles and a U.S. flag was set up in the center of the chapel in memory of the victims.
"As a mother myself, my heart really aches as if it happened to my own children," said Bang Myung-lan, a 48-year-old housewife, holding back tears. "As a Korean, I am deeply sorry for the deceased."
"Among the 32 killed were bright students who could have contributed greatly to society, and it's a big loss for all of us," Cardinal Nicolas Cheong Jin-suk told parishioners. "As a South Korean, I can't help feeling apologetic about how a Korean man caused such a shocking incident."
The cardinal said everyone should work together to prevent a recurrence of "such an unfortunate event."
"It is beyond my understanding how such a thing can occur - especially to think a Korean is responsible for this," said 68-year-old Lee Chun-ja after the service. "It really tears my heart. Something like this should never happen again."