Obama, who attended a memorial in Waco after first appearing with four of his predecessors at the dedication of the George W. Bush Presidential Library, spoke before a near-capacity crowd of 9,260 at the Ferrell Center on the Baylor University campus. Caskets of the 12 firefighters killed at the plant, each covered with a U.S. flag, were lined up in front of the stage.
In all, 15 people died and 200 were injured in last week's explosion at the West Fertilizer Co. plant.
"To the families and neighbors grappling with unbearable loss -- you are not alone. You are not forgotten," Obama said.
"We need people who so love their neighbors as themselves that they're willing to lay down their lives for them," Obama said of the volunteer firefighters who died.
Obama pledged the country will help West rebuild.
En route to the memorial. Obama's helicopter flew over the fertilizer plant and circled a few times.