OKLAHOMA CITY (AP) — Federal officials are resolved never to allow a terrorist attack like the Oklahoma City bombing happen again, Deputy Homeland Security Advisor Caitlin Durkovich told survivors and loved ones of the 168 people killed in the April 19, 1995, bombing Friday.

“What happened here in Oklahoma still rests heavy in our hearts; ... what transpired here 29 years years ago remains the deadliest act of homegrown terrorism in U.S. history,” Durkovich said in front of a field of 168 bronze chairs, each engraved with the name of a bombing victim, at the Oklahoma City National Memorial and Museum.

“Our collective resolve to never let this happen is how we bear witness to the memory and the legacy of those who were killed and those who survived” the bombing, Durkovich told the crowd of more than 100 people as a woman in the crowd wiped tears from her face.

The nearly hour-and-half long ceremony began with 168 seconds of silence for each of those killed and ended with the reading of the names of each of the victims.

Durkovich was joined by Secretary of the Interior Deb Haaland, Oklahoma Gov. Kevin Stitt and Oklahoma City Mayor David Holt for the ceremony on a partly sunny, cool and windy morning for the 29th anniversary of the attack on the Alfred P. Murrah Federal Building downtown.

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“This is a place where Americans killed Americans,” and the lessons learned after the bombing should be used to address the “political vitriol” of today, Holt said.

“We don’t want more places, and more days of remembrance. This should be enough,” Holt said.

The motives of the bombers included hate, intolerance, ignorance, bigotry, conspiracy theories, misinformation and “extreme political views,” Holt said.

Hatred of the federal government motivated former Army soldier Timothy McVeigh and co-conspirator, Terry Nichols, to commit the attack.

McVeigh’s hatred was specifically fueled by the government’s raid on the Branch Davidian religious sect near Waco, Texas, that left 76 people dead and a standoff in the mountains of Ruby Ridge, Idaho, that left a 14-year-old boy, his mother and a federal agent dead. He picked April 19 because it was the second anniversary of the Waco siege’s fiery end.

McVeigh was convicted, sentenced to death and executed by lethal injection in 2001. Nichols was sentenced to life in prison.

Stitt ordered American and state flags on state property to be flown at half-staff until 5 p.m. Friday in remembrance of those killed and injured in the bombing.

“As the world watched, Oklahomans banded together in a community-wide display of noble humanity,” Stitt said in a statement announcing the order.