"The two suspects involved in this horrible event were well-armed and ready to kill as many cops as they could," Gillespie said in the latest update of the investigation of the shooting that left officers Igor Soldo and Alyn Beck and Wal-Mart shopper Joseph Wilcox dead.
Wilcox was killed trying to draw his legal handgun to stop the Millers, who entered the store after shooting the officers eating lunch in the nearby restaurant.
The suspects "were prepared on that day to hunker down and stay in that Wal-Mart as long as they needed to," the sheriff said.
Gillespie wouldn't disclose more about a motive for the Millers' rampage and declined to say what was contained in a note left with a swastika symbol and a "Don't Tread on Me" flag in the pizza shop where the officers were ambushed.
He didn't say how many shots were fired in the CiCi's Pizza. That information was not immediately being made public, Sgt. John Sheahan said.
Gillespie said police still believe the Millers acted alone.
Police said previously the Millers shared an ideology with militia and white supremacists that law enforcement officers were oppressors. The couple was kicked out of an encampment of supporters of Nevada rancher Cliven Bundy, who engaged in an armed standoff in April with federal Bureau of Land Management agents trying to round up Bundy cattle in a public land trespassing dispute.
The Millers each had a handgun when they killed Soldo and Beck, and each took one of the officers' 9mm handguns and two spare clips of ammunition. The guns they brought with them were obtained by Amanda Miller in Indiana, where the couple lived before moving to Las Vegas in January.
Jerad Miller, 31, could not legally own weapons as a felon. He was convicted of vehicle theft in Washington state and had a criminal record in Indiana.
During the shootout in the Wal-Mart, a split-second exchange of gunfire changed the outcome of the fast-developing situation, Gillespie said.
Officer Brett Brosnahan came face to face with a surprised Amanda Miller rounding the corner of an aisle, and he wounded the 22-year-old assailant in the upper right shoulder.
Brosnahan wasn't hurt. He retreated before Jerad Miller, who had pulled a pistol-grip .12-gauge shotgun from his gym bag and donned a cloth vest and belt of shotgun shells, was mortally wounded in the chest by another police officer firing a military-style .223-caliber rifle.
Gillespie quoted Jerad Miller as declaring the start of a revolution and firing one shot into the ceiling after entering the Wal-Mart. He said the assailant shouted, "Stand down. You have failed. I am in charge now," as Sgt. Kurt McKenzie tried to get him to surrender near the back of the store.
Jerad Miller died lying prone on the floor. His wife lay nearby on her back, pointing a handgun at him before putting it to her own head and pulling the trigger. She was pronounced dead later at a hospital.