President Bush (l) and Laura Bush, second from left, Virginia Gov. Timothy M. Kaine (r) participate in a convocation to honor the victims of a shooting rampage at Virginia Tech, 17 Apr 2007

President Bush has paid tribute to the 32 people killed during a shooting rampage this week at a university in the eastern state of Virginia.

In his weekly Saturday radio address, Mr. Bush said millions of Americans are praying for the victims of that attack and for their families.  He said the tragedy at Virginia Tech University saddened the entire nation and cut short many promising lives.

But the president also noted that the killings brought a glimpse of what he called "humanity at its best," as many students risked their own safety to comfort their wounded classmates, and one teacher gave his life so that his students could escape the gunman.

The sister of the killer, Cho Seung-hui, issued a statement Friday saying he "made the world weep."  She said her family is heartbroken over the tragedy, and she apologized to the families of her brother's victims.

She said the family never knew he was capable of such actions, which she described as "unspeakable."

Her brother killed himself Monday after committing the worst shooting massacre in U.S. history.

Earlier Friday, people across the United States observed a day of mourning for the victims.  Saturday, hundreds of South Koreans held a candlelight vigil in Seoul for those killed at Virginia Tech.