Five police officers were killed and seven others wounded in the ambush. Two civilians were also hurt, the Dallas mayor's office said.  President Barack Obama said Saturday the reaction of the majority of Americans, protesters and police to the week's trio of tragedies showed a nation remarkably unified despite some views it is polarized on racial issues.  Americans of all stripes were outraged a "deranged" individual killed the five officers in Dallas just as American have deep concerns about police shootings in Louisiana and Minnesota,  , where he was attending a NATO conference.  "There is sorrow, there is anger and there is confusion about next steps but there is unity in that this is not how we want our communities to operate, this is not who we want to be as Americans," Obama said  For the president, that was grounds for optimism that the nation would move forward in a constructive way. He noted the scenes around the country were not akin to the polarized 1960s.  "You're not seeing riots and you're not seeing police going after people who are protesting peacefully," the president said.  "As tough, as hard, as depressing as the loss of life was this week, we have a foundation to build on. We just have to have confidence that we can build on the better angels of our nature."  Johnson had no criminal record or known terror ties, a law enforcement official said.  He served in the U.S. Army Reserve from March 2009 to April 2015, training as a carpentry and masonry specialist, according to Pentagon records. Johnson  , from late 2013, and received an honorable discharge.  Johnson had at least two weapons with him -- a rifle and a handgun, two law enforcement officials said.  One of the officials, familiar with the latest information from the Dallas police investigation, said the rifle was an SKS semi-automatic. The other official said Johnson legally bought multiple firearms in the past.  The killing of the five officers was  Dallas Police Officers Lorne Ahrens, a 14-year veteran of the department, and Michael Smith, a 27-year veteran, were both killed, according to local media reports and Smith's sister, who spoke to CNN affiliate KFDM.  CNN affiliate WDIV said Dallas officer Michael Krol was killed. The remaining two were Dallas officer Patrick Zamarripa and DART Police officer Brent Thompson.  Police have said at least 10 officers were shot by a sniper and one officer was shot in a shootout at the parking garage. It's not clear where the 12th officer was shot.  Three other shootings endangered police around the same time.  In Bristol, Tennessee, a man opened fire on motorists early Thursday at a motel and along the Volunteer Parkway, killing a woman and wounding three people, including a police officer, the Tennessee Bureau of Investigation said.  The TBI said the suspect, Lakeem Keon Scott, 37, may have targeted individuals and officers after being troubled by recent incidents involving African-Americans and police elsewhere. Scott was wounded by police, arrested and questioned at a hospital, the TBI said.  In metro St. Louis, a police officer was shot in the back of the neck Friday morning by a driver he stopped for a speeding, Ballwin Police Chief Kevin Scott said. The suspect was arrested and the officer was in critical condition, Scott said.  In Valdosta, Georgia, a police officer was shot Friday morning by a man who placed a 911 call to report a car break-in at an apartment building, the Georgia Bureau of Investigation said. The officer, who is in stable condition, was shot twice, the GBI said. The officer returned fire and wounded the shooter, who was identified as the caller and arrested.  Houston police said two officers killed a man whom they found standing in the middle of the street brandishing a revolver at 12:40 a.m. (1:40 a.m. ET).  The officers gave multiple commands for the man to drop the weapon, Houston police spokeswoman Jodi Silva said.  They talked to the man when he pointed the weapon in the air but shot and killed him when he pointed the weapon in their direction, she said.  The man was found with a revolver and there "are a number of witnesses" to the shooting, Silva said.  The man's race and identify were not immediately confirmed.  The police shooting in Minnesota claimed the life of  a 32-year-old school cafeteria supervisor. After what his fiancee described as a traffic stop for a broken taillight, she streamed the immediate aftermath live on Facebook.  Diamond Reynolds showed Castile groaning and bleeding in the front seat.  "He let the officer know that he had a firearm and he was reaching for his wallet and the officer just shot him in his arm," she said as she broadcast the Wednesday shooting on Facebook.  The attorney for Officer Jeronimo Yanez, who shot Castile, said the tragedy resulted from the presence of a gun.  "Regrettably, the use of force became necessary in reacting to the actions of the driver of a stopped vehicle. Officer Yanez is deeply saddened for the family and loved ones of Philando Castile," said attorney Thomas M. Kelly in a statement Saturday.  In Baton Rouge, Alton Sterling, 37, was killed Tuesday near a convenience store where he regularly sold CDs and DVDs.  A homeless man approached Sterling and asked for money, becoming so persistent that Sterling showed him his gun, a source told CNN.  The homeless man called 911 and police arrived at the store, tackled Sterling to the ground, and shot him several times, video shows.  CNN's Kevin Bohn, Brynn Gingras, Evan Perez, Shimon Prokupecz, Chuck Johnston, Barbara Starr, Madison Park, Hilary Whiteman, Sara Ganim, Khushbu Shah, Samira Said and Jason Hanna contributed to this report.
Dallas detectives piece together details of suspect Micah Xavier Johnson and whether he acted alone in the killing of five police officers during a protest.