Story highlights

Police searched a parking garage next to their headquarters for several hours

Cops say they used bomb on robot to kill suspect because they had no options left

CNN —  

Dallas police officers searched for hours for a suspicious person in the parking garage at their headquarters Saturday, the department tweeted.

The search yielded no suspects or strange items, the department said.

Officers and police dogs searched the three-story facility for several hours. It was unclear who reported the suspicious person.

The search came as visitors were dropping by the headquarters to pay tribute at a memorial for five police officers who were killed by a gunman Thursday night after a protest march.

Dallas police had tightened security throughout the city because of an anonymous threat, spokeswoman Monica Cordova said earlier without elaborating.

The search also came as Dallas police defended their use of bomb-carrying robot that killed Micah Xavier Johnson, the man who gunned down four Dallas police officers and one transit police officer this week.

The police department said it used the robot as a last resort.

Negotiations had failed and the gunman was still shooting at them, so police used C4 with a detonation cord mounted on a Remotec F-5 robot.

The explosive weighed about one pound, police said.

Ongoing investigation

Dallas detectives are piecing together a picture of Johnson to determine whether he acted alone in his ambush of police or had allies in preparing for the shooting that killed the five officers.

Authorities have said they believe Johnson was the sole gunman during the Black Lives Matter protest Thursday in Dallas. What is unclear is whether the 25-year-old army veteran, whom some people described as a loner, conspired with others or how long he had planned an attack.

Seven other officers were wounded in the ambush. Two civilians were also hurt, the Dallas mayor’s office said.

The shootings came amid a protest over the fatal police shootings of two black men in Louisiana and Minnesota this week. Similar protests – mostly peaceful – were held Friday in dozens of cities across the United States, and more are planned for Saturday.

Obama: Americans are united

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, said the President, speaking in Warsaw, Poland, 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.”

Who was Micah Xavier Johnson?

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 was deployed for about seven months in Afghanistan, 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.

Johnson’s last known employer was Jeppie Carnegie, who owns a home health care facility in Dallas. He told CNN he hired Johnson in January 2015. Carnegie said a background check showed no past criminal activity.

Johnson’s client was his own younger brother and he supported his sibling’s home living, Carnegie said. The Touch of Kindness owner told CNN he had infrequent interaction with Johnson, but always as professionals.

“Everyone was screaming, people were running,” said witness Clarissa Myles. “I saw at least probably 30 shots go off.”

The victims

The killing of the five officers was the deadliest single incident for U.S. law enforcement since September 11, 2001.

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.

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.

Other shootings of police

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 a preliminary investigation reveals the suspect, Lakeem Keon Scott, 37, may have targeted individuals and officers after being troubled by recent incidents involving African-Americans and law enforcement officers in other parts of the country. Witnesses said they heard someone yell, “Police suck! Black Lives Matter!” before bullets were fired, the TBI said.

In the St. Louis area, a police officer was shot in the back of his neck Friday morning by a suspect stopped for a speeding violation, Ballwin Police Chief Kevin Scott said. The officer was walking back to his patrol car when the suspect ran toward him, firing three shots from a semi-automatic handgun, Scott said. The suspect was arrested and the office was in critical condition, Scott said.

Saturday, the department identified the officer as Mike Flamion, who joined Ballwin’s force in December 2014 after seven years with police in De Soto, Missouri.

In Valdosta, Georgia, a police officer was shot Friday morning by a man who placed a 911 call, the Georgia Bureau of Investigation said. The officer, who is now in stable condition, went to an apartment complex to check on a reported car break-in and was shot twice when he exited his patrol vehicle, the GBI said.

The officer returned fire and wounded the shooter, who was identified as the caller and arrested. The man “wanted the police to shoot him” and “he wanted to die,” according to the Georgia Bureau of Investigation, citing interviews with suspect.

Man shot in Houston

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 ordered the man several times 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.

A revolver was found and there are a number of witnesses, Silva said.

The man’s race and identify were not immediately disclosed.

The protests

The police shooting in Minnesota claimed the life of Philando Castile, 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.

When can police shoot?

“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.

“Oh God, please don’t tell me my boyfriend is dead,” she said.

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.

Baton Rouge shooting

Sterling, 37, was killed Tuesday near a convenience store in Baton Rouge, where he regularly sold CDs and DVDs.

A homeless man approached Sterling on Tuesday 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. Police tackled Sterling to the ground, and shot him several times, video shows.

CNN’s Catherine E. Shoichet, Kevin Bohn, Brynn Gingras, Evan Perez, Shimon Prokupecz, Chuck Johnston, Barbara Starr, Madison Park, Hilary Whiteman, Sara Ganim, Khushbu Shah, Samira Said, Meridith Edwards, Devon Sayers and Jason Hanna contributed to this report.