Was Dallas cop killer Micah Johnson radicalized online?

(CNN)The message was clear. One day before Dallas police officers were gunned down, the African American Defense League was telling anyone reading its Facebook page it was time to act.

The message delivered at 9:47 a.m. Wednesday came after news broke of yet another killing of a black man by a white police officer. Philando Castile was killed in the front seat of his car after being pulled over for a broken taillight outside Minneapolis.
The message from the African American Defense League left little up for interpretation.
    "The Pig has shot and killed Alton Sterling in Baton Rouge, Louisiana!: You and I know what we must do and I don't mean marching, making a lot of noise, or attending conventions. We must "Rally The Troops!" It is time to visit Louisiana and hold a barbeque. The highlight of our occasion will be to sprinkle Pigs Blood!"
    The apparent author of that post, Mauricelm-Lei Millere, has so far not responded to CNN's request for comment. But from his Facebook page, CNN has discovered the killer of five Dallas police officers had visited and "liked" the AADL's site.
    Micah Johnson's online history shows he followed dozens of sites that focused on injustices committed on the black community. He visited and liked several websites dedicated to Black Lives Matter and the New Black Panthers, along with the Nation of Islam and the Black Riders Liberation Party, two groups the Southern Poverty Law Center considers hate groups.
    One friend who spoke to CNN said Johnson was obsessed with the plight of blacks in the United States and would repeatedly watch the now 25-year-old videotaped beating of Rodney King.
    "He was an expert on the history of the Martin Luther King assassination," the friend said. "And he studied Malcolm X."
    The friend, who did not want to be named, also said Johnson had issues controlling his temper. "He was a good black man with a little bit of an anger problem."
    Those who study the online radicalization of terrorists are seeing a similar pattern in the story of Johnson, a young man who may have been searching for identity and internalizing the hate and anger he was reading online.
    "Extremist groups generally use propaganda in the hopes of influencing people," said J.M. Berger of the George Washington University Program on Extremism. "They are trying to encourage lone wolf attacks where someone will carry out an attack in the name of the ideology they believe in but not have any connection to the organization that is promoting the ideology."
    Berger said it's a pattern that began with white supremacist groups 30 or 40 years ago. Terrorist groups like ISIS have taken the tactic online to social media. Now there is a concern groups considered black nationalist hate groups are employing the same tactics, and possibly inciting the same lone wolf style of violence.
    "It's not clear that they are pursuing that as an organized strategy. But certainly they are putting out incendiary content and if someone who is inclined toward violence is reading that, they may fixate on that content as a reason to take action," Berger said.
    One of those incendiary messages was posted then quickly deleted by the African American Defense League Thursday: "...calling on the gangs across the nation! Attack everything in blue..."
    We may never know what, if any, online messages inspired or incited Johnson to attack Dallas police, but Berger said it's not insignificant that he showed affinity for this material.
    On Thursday, the FBI sent a nationwide bulletin to law enforcement warning of online messaging that could inspire attacks against police. In the several-page warning, the FBI showed violent messaging that included the graphic depiction of a police officer's throat being cut.
    Tom Fuentes, a former associate director with the FBI, said the messages and those behind them should be treated the same way the federal government investigates ISIS.
    "It's no different than the ISIS propaganda that goes out," Fuentes said. "And the question
    for law enforcement is where do you draw the line between free speech and something else? If a message is espousing someone to take action, even if they inspire one guy to strike out, isn't that enough?"
    Fuentes said the FBI keeps track of hate groups online with the help of the Southern Poverty Law Center. But because the groups are mostly run by U.S. citizens, the FBI has larger barriers to what and how it can monitor groups protected by the right to free speech.
    Fuentes said it's a fine line and "some of these groups seem to be walking right up to that line."
    After the shootings and the death of Johnson, one of those Facebook sites devoted to the teachings of Elijah Mohammed took a page form the online playbook of ISIS and made the Dallas cop killer a martyr.
    The site posted Johnson's photo with the message, "R.I.P." for the man who "stood up to injustice."