Families, friends and strangers clung to each other during a 75-minute memorial service. They clutched flowers, blue and silver balloons and bibles as they wept and wondered why it happened.
"All of us must change our lives to honour these children," Mr Gore told the crowd a few blocks from where two teen-agers went on their murderous rampage. "More than ever, I realise every one of us is responsible for all of the children. No society can be perfect, but we know the way things should be," said Mr Gore, in the thunderous voice of a preacher.
As the Colorado state governor Bill Owens read the name of each of the 13 victims, a dove was released. "God grant them eternal peace," Mr Owens said. The symbol of peace had a special meaning: Columbine, Colorado's state flower, derives from a Latin word meaning "like a dove".
Mr Gore never mentioned by name the two students - Eric Harris and Dylan Klebold - who went on the rampage apparently because they felt like rejected misfits. But he told mourners: "I would be misleading you if I said I understand this. I don't know why human beings do evil.
"We must have the courage not to look away from those who feel despised and rejected. If you are a parent, they need your attention. If you are a grandparent, they need your time."
The service was punctuated by songs performed by a variety of Christian entertainers, including Amy Grant, and student musicians. Jonathan and Stephen Cohen, both Columbine students, sang a song they wrote in tribute to the victims. Jonathan, a third-year student, was trapped in the choir room when gunfire erupted. Stephen, in his final year, was in the cafeteria where many students were shot or hit by shrapnel from pipe-bombs.
"Can you still hear raging guns ending dreams of precious ones?" they sang. "In God's sun, hope will come, his red stain will take our pain."
Charles Chaput, the Roman Catholic Archbishop of Denver, told mourners: "Love is stronger than death ... Perhaps beyond all this suffering, something good can be achieved."