WASHINGTON (CNN) — Delaware Sen. Joe Biden doesn't think he'll be able to forgive the terrorists responsible for attacking the United States on September 11, 2001, he told CNN's Paula Zahn during an interview on his faith Monday night.

"You know, I wish I were a better Catholic," Biden said. "The answer to — the God's honest truth is, I have not been able to come to that conclusion yet. I have forgiven things that have happened to me, but in a sense, it's harder to forgive these major, major, major impositions of brutality on humanity."

While Biden acknowledged that forgiveness is a fundamental principle of his religion, he said it's hard to forgive people who indiscriminately harm or kill others. He also said he doesn't think God is taking sides in the war on terror.

"But I do think there is — it's not moral relativism," Biden said. "I think there's good and there's bad. There's evil and there's not. Those engaging in the brutal elimination of women and children, suicide bombers, I think God — I think there's a royal — I think there's a place in hell for them."

— CNN Associate Producer Lauren Kornreich