"And I freaked out, came in locked the door and from this window … you can actually see Norris Hall from here, and I saw a bunch of police officers running around with their guns," he explains.
Hong dove under the desk and hunkered down in his office for the next six hours. He feared for the safety of his students.
While Dr. Hong was locked in his office upstairs, his students were down in the basement, in the laboratory, with no windows, no cell phone service, and no clear picture of what was going on outside.
"I used one of these small cameras, Webcam, which has a magnet and clipped it outside my window," Hong explains.
He took a Webcam and pointed it towards Norris Hall, which gave his engineering students a high-tech, live video feed of what was happening right outside their building.
During these tense moments, one could see on Hong's video feed students running away and police officers with their guns drawn.
"It was very, very tense," Hong remembers.
Later, police brought him to the station, hoping he could identify the shooter.
Hong was shocked by the crime scene photos. "I don't want to describe, it was so horrific, I've never seen something that bad in my life," Hong tells Dow.
He did not recognize the shooter, and he was worried about the identity of the victims. "I'm just terrified that if I see one of the students that I know of or taught, I don't think I'll be able to handle it," Hong explains.
Tuesday, Hong returned to the lab with two students who had been trapped inside. And his students acknowledge that Hong's quick action provided them with one of the few links to the outside world.
for an interactive gallery of the victims.
"He did give us a link to the immediate outside world. Browsing Internet a lot, but only brief headlines, weren't very specific," one student tells Dow.
It seemed surreal: on Monday, the laboratory was the students' refuge from the horror they could see outside; normally, it's their place to tinker with the next generation of robots.
Hong, proud of his students and of his school, has lived in this usually serene community for four years. "Blackburg [is a] beautiful town. Lowest crime rate," Hong says. "Something like this happening, I never, never imagine."
His wife, So Young, also works on campus. At first, she could not reach husband and feared the worst. "When he contacted me by sending me an e-mail, it was a huge, huge relief, cause I was really, really worried," she recalls.
They are both safe now but reality is slowly sinking in.
Professor Hong now knows he lost two colleagues in the shooting; one was a good friend. "We just started to do collaboration together, we actually started a walking robot competition so we decided to have version of competition which students build, it would have been nice but, it's very difficult for me," Hong tells Dow.
When he learned the identity of the shooter, it also hit home. "It turns out he's Korean or Korean American student, and as I mentioned, me being a Korean Ameraican, it's quite shocking," Hong explains.
But Hong says he did not know the shooter, 23-year-old Cho Seung-Hui.
Dennis Hong admits he is disturbed by the news, but like many of the people in the Virginia Tech community, he believes that this incident, no matter how tragic, will not define the future.
"Can the school pull back together, can the school continue, go on?" Dow asks.
"I believe so, the Hokie Spirit, VA Tech, I'm sure it will rise again from this very difficult time," Hong says.