US President Barack Obama raises clasped hands with former President George W. Bush (L), first lady Michelle Obama and Dallas Mayor Mike Rawlings (R) during a memorial service for five policemen killed last week in a sniper attack in Dallas, Texas July 12, 2016. [Photo/Agencies]

"My heart is heavy. I'm tired of seeing my brothers and sisters killed, but the police don't deserve that," said Williams, who is black. "I'm praying that Obama being here brings us some kind of peace."

Chief Warren Asmus, a 35-year veteran with the Los Angeles County Sheriff's Department, said he flew in for the memorial.

"I was grateful for many of the things President Obama said in there," said Asmus, 57. "I need to understand what the black community goes through just as much as they need to understand what the police community goes through."

During his flight to Dallas, Obama placed condolence calls to families of Sterling and of Philando Castile, the 32-year-old man shot dead during a traffic stop outside St. Paul.