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President Obama arrived at a memorial service in Dallas Tuesday to address a city heartbroken by the deaths of five officers, reports the Washington Post .

Obama, speaking to a packed hall just a mile from where the gunman opened fire last week, invoked the names of the five police officers killed in the shooting rampage, describing details about each of their lives.

"Your work, the work of police officers across the country, is like no other," Obama said to a crowd filled with law enforcement officers from across the state and beyond. "From the moment you put on that uniform, you have answered a call that at any moment, even in the briefest interaction, may put your life in harm's way."

Obama said he has seen how inadequate words can be at spurring change, but said that if America "is to honor these five outstanding officers we lost," then the country must be honest about confronting its challenges going forward.

He rejected any suggestion that all police are biased or bigoted and pilloried people who, with their words, call for violence against officers. But he said that even though race relations have improved dramatically, "we know that bias remains." Still, Obama said that people simply cannot dismiss protesters and those questioning law enforcement tactics.

Obama echoed what Dallas police Chief David Brown said a day earlier about officers being asked to take on too much, saying that too great a burden is placed on police departments.

"We tell them to keep those neighborhoods in check at all costs and do so without causing any political blowback or inconvenience," he said. "'Don't make a mistake that might disturb our own piece of mind,' and then we feign surprise when periodically the tensions boil over."

Five seats in the service were left open in memory of the officers killed in Dallas last week, reserved for those who “died for that cause” of protecting others, Mayor Mike Rawlings said during his remarks.

Dallas police officers and other first responders were among those filling the 2,000 seats in the Morton H. Meyerson Symphony Center, along with the families of the officers killed and injured in last week's attack and two civilians who were wounded, city spokeswoman Patricia Blasquez told CNN .

During the program, Obama praised police for protecting and serving the people.

"Like police officers across the country, these men and their families shared a commitment to something larger than themselves," the President said. "... The reward comes in knowing that our entire way of life in America depends on the rule of law, that the maintenance of that law is a hard and daily labor, that in this country, we don't have soldiers in the streets or militias setting the rules. Instead, we have public servants, police officers, like the men who were taken away from us."

Police in Dallas "showed incredible restraint" and "saved more lives than we will ever know," Obama said.

"When the bullets started flying, the men and women of the Dallas police, they did not flinch, and they did not act recklessly," he said.

George W. Bush also spoke at the memorial service. The former president, who lives in Dallas, said the slain officers were the "best among us." With their death, Bush said Dallasites – and Americans all over – are "grief-stricken, heartbroken and forever grateful," reports the Dallas Morning News .

Bush called for unity and then looked to law enforcement.

"We know that the kind of just, humane country that we want to build, that we have seen in our best dreams is made possible when men and women in uniform stand guard," he said. "At their best, when they are trained, trusted and accountable, they free us from fear."

The former president concluded by speaking directly to the families of the fallen officers.

"Your loss is unfair. We cannot explain it," he said. "We can stand beside you and share your grief. And we can pray that God will comfort you with a hope deeper than sorrow and stronger than death."