"It gave me hope because I was in a very dark place at that point in time," he recalled.
Dempsey lost friends in the towers and nearly lost his own life.
"I felt the impact full blast," he said.
Dempsey was working in Five World Trade Center when the first plane hit. He escaped and then tried calling his wife who normally works in the first tower but thankfully was running late that day.
Then the second plane hit and the crowd trampled him.
"I had internal bleeding. I had fractured skull and other injuries. So, It was hard being a survivor, I was like why am I here," he said.
There's been survivor's guilt, pain, and an emotional journey since. During the near decade since the attacks, he's thought about Osama bin Laden and al-Qaida.
"Osama bin Laden represents the figurehead. He's the financier," said Dempsey.
And now that he's dead, Dempsey calls the news bittersweet.
"I felt justice, but I think the other thing that came to mind was 'Do I get closure out of this?' I don't feel like there was any closure," said Dempsey.
No closure dempsey says because for most 9/11 families there were no remains recovered from Ground Zero - nothing to bury. And, said bin Laden's death doesn't bring back the ones they've lost.
Dempsey now organizes 9/11 family events and works with Oklahoma City bombing families too.
He said there's never a sense of closure when you're a victim of terrorism.