Speaking at a memorial for 12 workers who died in the Washington Navy Yard rampage last week, he urged the U.S. not to accept mass shootings as routine. This, Obama noted, is the fifth time he has grieved with communities "ripped apart by mass violence" since taking office in January 2009.
"Once more our hearts are broken," he told the more than 5,000 people who attended the service at the Marine Barracks Washington, a few blocks from the Navy Yard. "Once more we ask, why? Once more we seek strength and wisdom through God's grace."
Speaking to family and friends of the fallen, he said, "There is nothing routine about your loss."
When other nations experienced mass shootings, Obama said, they came together to find a way to stop them. But that has yet to happen in the U.S., he said, where obtaining guns is easier.
"These families have endured a shattering tragedy," he said. "It ought to be a shock to all of us as a nation and as a people. It ought to upset us. It ought to lead to some sort of transformation."
The U.S. murder rate is three times that of other developed nations, he said, and the murder rate with guns is 10 times that of other developed nations.
"No other advanced nation endures this kind of violence. None," he said.
Officials say Navy contractor Aaron Alexis, 34, shot 12 people to death at the Navy Yard last Monday before he was killed by police. The victims ranged in age from 46 to 73 and included civilians who worked at the Navy Yard as well as former service members.
"These are not statistics," Obama said. "They are the lives that have been taken from us."
The president and first lady met with victims' families before the service, which was not open to the public.
During the memorial, Obama illustrated the families' losses with vignettes about the victims, including John Johnson, 73.
"John Johnson looked at his wife, Judy, and said what he always said whenever they parted," Obama said. " 'Goodbye, beautiful, I love you so much.' "