A US Air Force sergeant with links to the far-right “boogaloo” movement has been charged with the murder of a federal security officer in California, the FBI says.
Steven Carrillo is accused of killing David Patrick Underwood outside the courthouse in Oakland during Black Lives Matter protests last month.
He was already charged with the murder of another officer eight days later.
Damon Gutzwiller was killed in an ambush near Santa Cruz on 6 June.
Mr Carrillo, who is stationed at Travis air force base, was arrested during a subsequent confrontation.
He appears to have used his own blood to write various phrases on the bonnet of a car he stole, the FBI said, including “boog” and “stop the duopoly”.
“Boogaloo” is a term used by extremists to reference a violent uprising or impending civil war in the US, the FBI said.
Adherents of the loose grouping, which some liken to a militia, are anti-government and often carry assault weapons and support the idea of a race war.
The Oakland victim, Mr Underwood, was killed in a drive-by shooting from a white van overnight on 29 May. There were large protests taking place in nearby streets over the death in police custody of George Floyd.
A colleague was also shot in the attack, and the accused is charged with his attempted murder.
A second man, Robert Alvin Justus, has confessed to driving the van, the FBI said, and has been charged with aiding and abetting the alleged murder.
In a comment on Facebook, Mr Carillo said the Black Lives Matter protests in downtown Oakland were a good opportunity. “Use their anger to fuel our fire. Think outside the box. We have mobs of angry people to use to our advantage,” he allegedly wrote.
Announcing the charges at the same Oakland federal building where Mr Underwood worked, US Attorney David Anderson said many people would miss hearing the sound of his voice and laughter.
“Pat Underwood wore his uniform because it signified his authority to protect the courthouse where we are gathered here today,” the attorney said. “This courthouse exists to administer justice, to uphold the rule of law, and to protect the freedoms that we all cherish.”
A second deputy was injured in the attack in Santa Cruz county in which Sgt Gutzwiller lost his life.
The sheriff’s office is holding a memorial event for Sgt Gutzwiller on Wednesday which will be broadcast online.