In May 2020, as protests over the death of George Floyd raged across the country, federal security officer Dave Patrick Underwood was shot and killed while protecting the federal courthouse in Oakland, California.

       The alleged shooter, Steven Carrillo, an active-duty Air Force staff sergeant, carried a ballistic vest with a patch that featured an igloo and a Hawaiian-style print that are both associated with the far-right anti-government boogaloo movement, according to the federal criminal complaint.

       The criminal complaint also said Carrillo --- who was charged with murder and pleaded not guilty -- used his own blood to scrawl “boog” on the hood of a vehicle and met an accomplice online through a Facebook group centered on the boogaloo movement.

       Now, Underwood’s sister, Angela, is suing Facebook in California Superior Court, alleging the company used its algorithms and group function to actively recruit members for far-right extremist groups and promote dangerous content. Her lawsuit also alleges Facebook ignored the foreseeable risk of violence in order to maximize profits and united Carrillo and his alleged accomplice -- two people it says would otherwise have not known each other.

       Promoting extremist activity, the lawsuit said, contributed to Underwood’s death.

       "The shooting was not a random act of violence. It was the culmination of an extremist plot hatched and planned on Facebook by two men who Meta [Facebook's new company name] connected through Facebook’s groups infrastructure and its use of algorithms designed and intended to increase user engagement and, correspondingly, Meta’s profits," the civil complaint, filed in Alameda County, said.

       MORE: Suspect in sergeant's slaying now charged in killing of federal officer in Oakland: Officials

       Shmuel Thaler/The Santa Cruz Sentinel via AP, FILE

       California Highway Patrol officers keep a road closed in Ben Lomond near Santa Cruz, Calif., June 8, 2020, as FBI agents continue processing the scene where Santa Cruz County Sheriff's Sgt. Damon Gutzwiller was killed. Staff Sgt. Steven Carrillo has been arrested on suspicion of fatally shooting Gutzwiller and wounding two other officers.

       “Facebook bears responsibility for the murder of my brother,” Angela Underwood Jacobs said in a statement. “Facebook knowingly promoted inflammatory and violent content and connected extremists who plotted and carried out the killing of my brother. Facebook must be held responsible for the harm it has caused not just my family, but so many others through its promotion of extremist content and by promoting algorithms to actively recruit members to its web platform.”

       Her attorney, Ted Leopold, cited whistleblower testimony before Congress that accused Facebook of knowingly encouraging and promoting extremist content.

       “We believe and intend to show that Facebook’s conduct has led to a rise in extremism throughout the world and acts of real-world violence, including the murder of Officer Underwood,” Leopold said.

       Earlier this year, Facebook said it has taken measures to counter hate and extremism online.

       MORE: Facebook whistleblower documents offer new revelations about Jan. 6 response

       And in testimony before Congress in March, CEO Mark Zuckerberg said "the vast majority of what people see on Facebook is neither political nor hateful" and that "we work hard to prevent abuse of our platform."

       "Facebook’s mission is to bring people together, and we stand firmly against hate and the incitement of violence," Zuckerberg testified. "We have industry-leading policies that prohibit such content on our platforms, and we invest billions of dollars and work tirelessly to improve and enforce these policies."

       In June 2020, Facebook said it removed more than 200 accounts associated with a "violent US-based anti-government network" that "uses the term boogaloo but is distinct from the broader and loosely-affiliated boogaloo movement."

       "For months, we have removed boogaloo content when there is a clear connection to violence or a credible threat to public safety, and today’s designation will mean we remove more content going forward, including Facebook Groups and Pages," the statement said.

       In Boogaloo Facebook groups, the suspect, Carrillo, mused about taking advantage of protests to stir up unrest and violence against police, according to the civil complaint which quoted his post: “Go to the riots and support our own cause. Show them the real targets. Use their anger to fuel our fire. Think outside the box. We have mobs of angry people to use to our advantage.”

       Carrillo believed that the Boogaloo, or second civil war, was “kicking off now and if its not kicking off in your hood then start it,” according to the civil complaint.