JUDY WOODRUFF: Finally tonight: something we just heard touched on, the Oklahoma City bombing 15 years later. "NewsHour" correspondent Kwame Holman has the story.
KWAME HOLMAN: It has become an annual tradition. Hundreds of survivors and family members of the victims gathered again today. They met at the Oklahoma City National Memorial, which includes the site where the Alfred P. Murrah building stood. On the morning of April 19, 1995, a huge truck bomb exploded just outside the Murrah Building.
MAN: I went under the table when the ceiling started to fall in.
KWAME HOLMAN: It killed 168 people and wounded more than 600 others. The enormous blast also damaged hundreds of millions of dollars of property. Today, Mayor Mick Cornett said the city refused to let that day be an end.
MICK CORNETT, mayor, Oklahoma City: We have chosen strength. We have chosen optimism. We have chosen freedom. And we have chosen to move forward together with a level of unity that is unmatched in any American city.
KWAME HOLMAN: The principal figure behind the attack was Timothy McVeigh, a U.S. Army veteran and former security guard. He said he was seeking revenge against a tyrannical federal government. He was convicted on federal murder charges and executed in 2001.
MAN: The system works. And America is good.
KWAME HOLMAN: McVeigh's accomplice, Terry Nichols, was convicted on federal and state bomb-related charges. He's serving multiple life sentences at a federal prison in Colorado. The plot unraveled almost immediately when McVeigh was stopped a few hours after the bombing because his car had no license plate. The state trooper who made the arrest, Charlie Hanger, now is a county sheriff. He led a moment of silence today.
CHARLIE HANGER, sheriff, Noble County, Oklahoma: We come here to remember those who were killed, those who survived, and those changed forever. May all who leave here know the impact of violence. May this memorial offer comfort, strength, peace, hope, and serenity. Please join me in 168 seconds of silence.
KWAME HOLMAN: And, as they do every year, relatives read the roll call of the dead.
BOY: My grandpa, Mickey B. Maroney.
WOMAN: My mother, rescue worker Rebecca Needham Anderson.
MAN: My brother, Captain Randolph A. Guzman.
WOMAN: My sister, Robin Ann Huff and baby Amber Denise Huff.
KWAME HOLMAN: The Oklahoma City bombing still stands as the most destructive act of domestic terrorism in American history. The secretary of homeland security, Janet Napolitano, warned today of the need for continued vigilance.
JANET NAPOLITANO, U.S. Homeland Security Secretary: We control the way we prepare ourselves, the way we combat threats, and the way we respond if something indeed happens. America is a strong nation. We are a resilient nation. And, as we confront new threats, we will use our values and our way of life as the most powerful sources of our strength. We will do this for now and for years to come.
KWAME HOLMAN: After today's ceremony, many of the family members passed by the memorial's empty chairs representing those lost. And they paused near a large American elm dubbed "The Survivor Tree" because it withstood the blast 15 years ago. Under a state law signed this month, the bombing and its aftermath will become a regular part of history classes in Oklahoma's schools.