Twenty years ago today, Timothy McVeigh — an Army veteran with strong anti-government views — drove a rental truck containing a massive homemade bomb up to the front of the Alfred P. Murrah Federal Building in Oklahoma City, lit the fuse and walked away.

The result was the worst act of domestic terrorism in U.S. history. It took the lives of 168 people, including many children attending a daycare in the targeted building.

Survivors and relatives of the dead gathered to remember that day and time — April 19, 1995 at 9:02 a.m. that the bomb detonated. The service included a 168-second moment of silence in memory of the victims.

Former President Bill Clinton, who was in the White House when the attack took place, said "it's important to remember ... how much Americans owe to Oklahoma City."

The city's residents, he said "had to choose to affirm our common humanity in the face of mad, crazy people who believe that the differences are all that matter enough to dehumanize innocent bystanders," Clinton said.

Oklahoma Gov. Mary Fallin also spoke at the ceremony.

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