Steven Carrillo pleads not guilty to murder of Oakland federal Ofc. Pat Underwood

OAKLAND, Calif. (KGO) -- Thirty-two-year-old Steven Carrillo pleaded not guilty Thursday morning in Oakland Federal Court to the murder of a federal protective services officer, 53-year-old Pat Underwood, on May 29 and to the attempted murder of his partner, who survived the attack.

RELATED: Steven Carrillo charged in Oakland, Santa Cruz Co. officer killings linked to Boogaloo movement, federal investigators say

He spoke only once when Judge Nathaniel Cousins asked, "Do you understand the charges against you?" Carrillo, in a red inmate's shirt, answered by Zoom from Santa Rita Jail in Dublin with a clear "yes."

Carrillo could receive the death penalty or life in prison if convicted. His next hearing is August 6.

RELATED: Federal officer shooting suspects Steven Carrillo, Robert Justus 'came to Oakland to kill cops,' FBI says

Carrillo is accused of killing Underwood by opening fire from a white van at the Oakland Federal Building's security post. Thirty-year-old Robert Justus is accused of driving the van at the time.

Federal agents say the same van and gun were part of the ambush that killed Santa Cruz County Sheriff's Deputy Damon Gutzwiller on June 6. The criminal complaint says Carrillo's ballistic vest he had that day bore a patch, a symbol of the "boogaloo" movement, what the US Attorney described as extremists who believe in an impending civil war.

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