U.S. Attorney General Loretta Lynch said Friday the Dallas shooting where five police were slain will be treated as the first-ever federal hate crime investigation centered on a cop killing. Lynch revealed details of the next phase into the investigation during a nationally televised press briefing.

“This has been a week of profound grief and heartbreaking loss,” Lynch said. “After the events of this week, Americans across the country are feeling a sense of helplessness, and uncertainty and of fear.”

The killing of five police officers in Dallas occurred the same week as the nation learned of the fatal shootings of two black men at the hands of police. Alton Sterling was killed in Louisiana while selling CDs outside a convenience store while Philando Castile was killed in Minnesota over what began as a traffic stop over a broken tail light.

Even while making the announcement, Lynch appealed for calm.

“After the events of this week, Americans across the county are feeling a sense of helplessness, of uncertainty and of fear. These feelings are understandable and they are justified. But the answer must not be violence. The answer is never violence.”

Instead, the reaction should be one aimed at peace: “Rather, the answer must be action: calm, peaceful, collaborative and determined action. We must continue working to build trust between communities and law enforcement. We must continue working to guarantee every person in this country equal justice under the law. We must take a hard look at the ease with which wrongdoers can get their hands on deadly weapons and the frequency with which they use them. We must reflect on the kind of country we want to build and the kind of society we want to pass on to our children.”

She offered her condolences to those affected.

“To the families of all who lost their lives in this series of tragedies, we share your pain and your loss. To our brothers and sisters who wear the badge: I want you to know that I am deeply grateful for the difficult and dangerous work you do every day to keep our streets safe and our nations secure. I am heartbroken at this loss. And the Department of Justice will do all we can to support you in the days ahead.”

Dallas Police Department Chief David Brown on Friday described the attack as a “well-planned, well-thought-out, evil tragedy” during a press conference. “We won’t rest until we bring everyone to justice.”

A glance at his Facebook page illustrates the methodical nature of Johnson’s actions, where his fomenting anger is in full display: “Attack everything in blue,” he wrote in one post.

A police search of his home yielded the tools attendant to that hatred.

“During the search of the suspect’s home, detectives found bomb-making materials, ballistic vests, rifles, ammunition, and a personal journal of combat tactics,” Dallas Police Department officials said. “Detectives are in the process of analyzing the information contained in the journal.”

So far, detectives have interviewed more than 200 officers, DPD officials said. Based on those interviews, it’s been determined that at least 12 officers discharged their weapons during their confrontation with Johnson.

The full spectrum of law enforcement is now investigating the crime scene Johnson left in his wake, the DPD said: The Bureau of Alcohol, Tobacco, Firearms, and Explosives; the Federal Bureau of Investigation; U.S. Marshals; Homeland Security Investigations; Drug Enforcement Administration; Department of Public Safety; Texas Rangers; Dallas Area Rapid Transit; Dallas County District Attorney’s Office; and the Dallas County Sheriff;s

The agencies, the DPD said. “…are all assisting with the investigation and the processing of evidence and crime scene locations.”

As a result of the massive crime scene, portions of the area are expected to be closed to the public until at least Wednesday, APD officials said.

In their statement Friday updating the media on their investigation, DPD noted Johnson had no criminal history.

“Information provided through the course of the investigation indicates that the suspect was an Army veteran, and others have identified him as a loner,” police wrote.

They referenced his Facebook page — the account that has been scoured for clues into Johnson’s motivations by untold numbers of journalists and others.

“The suspect’s Facebook account included the following names and information: Fahed Hassen, Richard Griffin aka Professor Griff. Griffin embraces a radial form of Afrocentrism, and Griffin wrote a book “A Warrior’s Tapestry.”

Police noted that another suspect was arrested for unrelated weapons charges, but didn’t indicate if the person was in any way involved in the attack. They identified the person detained as Brandon Waller, a 25-year-old black male, who was arrested on the night of the attack July 7.

DPD Chief Brown described the pain being felt throughout the rank-and-file in the worst loss of law enforcement officers since 911: “We’re hurting. Our profession is hurting. Dallas officers are hurting. We are heartbroken. There are no words to describe the atrocity that occurred to our city.”

In their statement, DPD echoed Brown’s sentiments: “We are so thankful for the overwhelming prayers, support, love, and donations from everyone,” officers wrote. “Please continue to keep the families of the officers in your thoughts and prayers. Out of respect for the families of the fallen and injured officers, the Dallas Police Department is waiting to officially release their names pending approval from the family members.”

Meanwhile, prominent voices have reacted to the crime. Some of the reactions strike a conciliatory tone calling for peace while others urge the tactics of returning law and order to the streets.

The day after the massacre, Gov. Greg Abbott penned an “open letter to Texans” published in the Dallas Morning News.

“The coordinated ambush and deliberate, brutal executions were acts of cowardice — hiding behind innocents to target and savagely slaughter peace officers dedicated to preserving life and our freedoms,” Abbott wrote. “The full force of the law must ensure all responsible are brought to justice and our communities are kept secure. Justice will be served, but justice is small solace for the families left behind.”

In a time of increasing polarization, Abbott called for unity.

“It is time for us to unite as Texans, as Americans, to say no more,” he wrote. “No more will we tolerate disrespect for those who serve. No more will we allow the evil of hate merchants to tear us apart. Though anguish and sorrow may darken the days ahead, we will not be overcome by evil – we will overcome evil with good.”

The two presumptive nominees for president, Hillary Clinton and Donald Trump, each struck contrasting notes in their own reactions to the tragedy.

“We must restore law and order,” Trump said in a prepared statement. “We must restore the confidence of our people to be safe and secure in their homes and on the street.”

Clinton plans to address the attacks Friday evening at the African Methodist Episcopal Church conference n Philadelphia, but not before she conveyed her condolences to those impacted.

“I mourn for the officers shot while doing their sacred duty to protect peaceful protesters, for their families and all who serve with them,” she wrote Friday on Twitter.

According to the New York Times, Clinton has postponed a rally with Vice President Joe Biden in Scranton, Pennsylvania, that had been scheduled for Friday in order to address the tragedy later tonight.

President Barack Obama condemned the killings, addressing the nation from Poland where he was attending a NATO summit.

“Police in Dallas were on duty, doing their jobs, keeping people safe during peaceful protests,” he said. “I believe I speak for every single American when I say we are horrified and we stand united with the people and police department in Dallas.”

Obama categorized the attack as “vicious” and “calculating.”

The president issued a proclamation on Friday, ordering flags to be flown at half-staff at the White House, all public buildings and military posts throughout the country.

“I also direct that the flag shall be flown at half-staff for the same length of time at all United States embassies, legations, consular offices, and other facilities abroad, including all military facilities and naval vessels and stations,” Obama’s proclamation reads.

Even in the post-attack moments when calm has returned to downtown Dallas while people try to make sense of what transpired, Dallas police stress the investigation is ongoing. They urge any members of the public who may have information that might assist them in their investigation to call them.

The APD telephone number to call with tips or insights into the crime is (214) 671-3584.