At least 1,000 people attended the 90-minute vigil, organized by gun-safety advocates, the Washington Post reported.
Bells rang for 3 minutes at the start of the vigil, each minute representing 10,000 of the more than 30,000 people who died from gun violence last year, the newspaper said.
About 100 residents of Newtown were brought in by buses to join thousands of family members from across the country who have been directly affected by gun violence.
A string of relatives of the dead came forward to speak of their lost loved ones.
"Those who've gathered here today show me that my family is not standing alone," said 15-year-old Anthony Hardmond, holding a photo of his older sister Ashley, who was gunned down on a Chicago street. "I will remember."
As with each speaker, the congregants responded, "We will remember."
"A year ago next Sunday, I said from this pulpit, 'The gun lobby is no match for the cross lobby,'" the Very Rev. Gary Hall, dean of the Washington National Cathedral, said. "I said that then, and I say it now. I believe that the forces of love are greater and stronger than the forces of hatred. ...
"As Christians, we follow one who died at the hands of human violence," Hall said. "We call our elected leaders to find the moral courage and the political will to lead us all into a new, safer, era in American history. Make us instruments of your peace, and strengthen our hearts and hands and minds not only to care for the victims and survivors of gun violence but also to bring about the change that will end the violence caused by guns in the hands of the criminal, the sick, and the cruel."
On Dec. 14, 2012, gunman Adam Lanza fatally shot 20 children and six adult staff members at Sandy Hook Elementary School in Newtown.
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