On April 3, Wong walked into the American Civic Association and opened fire with two handguns, killing 13 people and wounding four others before committing suicide.
Voong said his son kept to himself and rarely interacted with his family despite living in the same house in Johnson City, near Binghamton. He did not have any friends and rarely spoke to anyone, they said.
To them, he lived a quiet, nearly silent existence for the last 19 years.
According to his father, that silence deepened two weeks before the shooting. Wong stopped eating dinner, stopped watching television and rarely emerged from behind his bedroom door.
"He avoided being in the house at the same time with me," Voong told the newspaper. "At first, I thought maybe he was mad about something and was planning to ask him. This tragedy occurred before I even had a chance to ask him."
Voong and Thong say they didn't learn of their son's role in the shootings until reading about it in a newspaper the next day.
The Voongs remain concerned that someone will take out revenge on them. On Friday, clergy and local officials planted 14 tulips in a memorial garden to remember the 14 people who died in the rampage. Over the weekend, someone uprooted the 14th tulip, police said.
The newspaper said the couple contacted The Post-Standard on Thursday because they wanted to apologize to the Binghamton community and all those affected by their son's actions. In an interview conducted in Vietnamese, Voong, 66, and Mui Thong, 61, said they don't know if their son suffered from mental illness.
An incident 19 years ago was the only time Voong witnessed his son behave erratically, the father said. At that time, Wong told his father he believed someone was trying to kill him. Voong said he took his son to a hospital, but doctors sent him home after two hours, saying they could find nothing wrong with him.
On April 6, a letter written by Wong arrived at a Syracuse TV station. Wong wrote that undercover police officers taunted him, tortured him and spread rumors about him wherever he went.
Voong said he has never seen any officers calling or visiting his son.
Voong and Thong say they ultimately don't know why their son killed so many.
"All parents raise their children to be good human beings," Voong said. "You never imagine in your wildest dreams that they would end up doing something so horrific."
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