DALLAS - President Obama and the nation are paying tribute Tuesday afternoon to the five police officers killed in last week's ambush in Dallas. Obama was to attend and speak at a private, interfaith memorial service, and former President George W. Bush was also to deliver remarks. Both will meet with victims' families.

Five empty chairs holding American flags represented Michael Smith, Lorne Ahrens, Michael Krol, Brent Thompson and Patrick Zamarripa.  

Dallas Mayor Mike Rawlings spoke first, bringing the crowd to their feet as he expressed awe of his city law enforcement officers. 

The slain officers were also honored during a vigil outside City Hall in Dallas.

Among the speakers, the city's heartbroken Police Chief David Brown who called the officers superheroes. Three of the fallen police officers will be laid to rest this week.

When asked what young black men can do to overcome their fear of cops, Brown said, "We're hiring."

"Get off that protest line and put an application in," he said. "We will help you resolve some of the problems you're protesting about."

As the city mourns, the family of the gunman have become central to the investigation. Investigators have questioned the former Army Reservist's relatives about a stockpile of bomb-making equipment found in his home.