On May 29, 2020, Air Force Sergeant Steven Carrillo and Robert Alvin Justus Junior drove to the Oakland protests in the wake of George Floyd's murder. Officer Dave Patrick Underwood was standing guard outside a federal courthouse. According to a criminal complaint, Carrillo fired multiple rounds at Underwood killing him.
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"I miss being able to pick up the phone and talk to my brother, I miss laughing with my brother, I miss hearing funny stories that he would tell. I miss him," said Angela Underwood Jacobs.
Carrillo is accused of also shooting and killing Santa Cruz Sheriff's Deputy Sgt. Damon Gutzwiller before being arrested.
According to a criminal complaint, Carrillo and Justus met online through a Facebook group centered on the boogaloo movement which federal prosecutors have said extremists use to reference a violent uprising or impending civil war in the United States.
"This is what I came here to fight. I'm sick of these (expletive) police," Carrillo said while being arrested.
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As Carrillo and Justus await trial on federal criminal charges, Underwood's sister Angela is now suing Meta Platforms, Incorporated, formerly Facebook, alleging the social media platform connects users to extremist groups and promotes inflammatory, divisive and untrue content.
"Had it not been for Facebook they might have never met," she said.
"Why should Facebook not be held accountable I believe they should," she continued.
Underwood's attorney, Ted Leopold anticipates Facebook will seek to shield itself from the litigation.
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"They are much more than a publisher they are an active participant and they are recruiting people to come onto their sites and once they are on their sites they use a lot of different algorithms that will bring like minded individuals together," said Leopold.
"Facebook knows it they were monitoring this and they did nothing," he continued.
David Greene, Civil Liberties Director at the Electronic Frontier Foundation says lawsuits like this one can be difficult to win.
"It's really hard both from a first amendment perspective and a statutory perspective to actually hold these internet platforms responsible," said Greene.
In an emailed statement to ABC7 News, a Facebook Spokesperson writes, "We've banned more than 1,000 militarized social movements from our platform and work closely with experts to address the broader issue of internet radicalization. These claims are without legal basis."
WATCH: David Patrick Underwood's family and friends talk to ABC7's Anser Hassan before Underwood's memorial
Meantime, Underwood's sister says she wants her brother to be remembered for his heart of gold.
"My brother stood for something which is honesty, integrity, a sense of community, loyalty and dedication," said Underwood Jacobs.
Justus' criminal defense attorney tells ABC7 News the trial for Justus and Carrillo is scheduled for April of 2023.