(CNN) -- Filled with regret, Kelley Fielder wishes she would have tried to stop them.
She was Amanda Miller's best friend. Amanda and her husband, Jerad Miller, had moved from Indiana to Las Vegas and for two weeks had been living with Fielder.
Jerad was always going off, she recalled, spewing anti-government rants. He filled his Facebook page with political cartoons that mocked police and other authorities. A recent post read: 'We must ... prepare for war."
Then something really disturbing.
Around 5:45 Sunday morning, Fielder told CNN, the couple were awake. They had a cart full of ammunition.
What were they doing? she asked.
They told her they were "going underground," Fielder said.
"The revolution has begun," Jerad Miller told Fielder.
"I should have called the cops," she said Monday. "I'm so, so, so sorry -- to everybody. I'm sorry."
On Tuesday, Carie Stichter, Jerad Miller's mother, released a statement.
"We wish to express our greatest sympathies, thoughts and prayers to the families who have lost their loved ones in this horrible act of violence. We are profoundly saddened, confused and in shock over the senseless actions of our son and his wife. We ask that the media respect our family's privacy during this ... difficult time."
Bystander went after Jerad Miller
Within hours of Fielder's exchange with Amanda, 22, and Jerad, 31, the couple had shot to death two police officers and a bystander who apparently tried stop their rampage.
That man, Joseph Wilcox, was with Jeremy Tanner, a longtime friend at a Las Vegas Walmart when the Millers walked through the door. Tanner recalled seeing Jerad Miller come into the store, seeing Miller dressed in some kind of fatigues and wearing gear.
Tanner had to very quickly process what was happening.
He heard Miller shout, "This is the beginning of the revolution! Everybody get out! You will be shot!"
Tanner looked at his friend Wilcox. He knew Wilcox had a concealed carry permit and sometimes had a gun on him. Customers and staff were fleeing the store.
Wilcox "had the option to go left to exit the store to safety," Tanner told CNN. But he chose not to leave. Wilcox instead stayed inside and confronted Jerad Miller, Tanner said.
Tanner told CNN his friend was unaware that Jerad Miller was with Amanda Miller. Wilcox was shot, authorities said.
The couple retreated toward the back of the store, where police closed in.
Amanda Miller shot her husband and then herself, police said. They both died.
It was hours before Tanner was told that his friend was killed. He is devastated, he told CNN. Sunday's violence made him "ashamed for the human race ... that people just have total disrespect for themselves and other people."
He can't stop thinking about it. What if he'd changed his schedule a little bit that day? What if he and his friend had not been in that Walmart at that time?
"You never expect it," he said. "It's something you see on TV, in the movies. ... "
Wilcox's 18-year-old sister, C.J. Foster, told CNN that she felt her brother was brave for attempting to interfere.
"I'm very proud of him," she told CNN. "I would have never done it. I would have never. I would have froze in place probably and the fact that he just rushed in after and tried to save those people, it was heroic."
Two officers slain
Wilcox was the Millers' third victim.
Their rampage began when they walked into a CiCi's Pizza place around 11:30 a.m. in a non-glitzy part of the city where two police officers were having lunch.
The couple shot Igor Soldo, 31, in the back of the head, and Alyn Beck, 41, took a bullet to the neck, authorities said.
On Tuesday, Beck friend Tracy Smith remembered the officer in an opinion piece for CNN.com. Officer Beck was kind and funny, intelligent, a tireless worker and a devoted husband and father of three. He loved his dog, Marty, she wrote.
Soldo was married and had a baby.
The Millers placed a "Don't Tread on Me" flag and a Nazi swastika on one officer's body, authorities told reporters Tuesday.
On the other officer's body, authorities said, a note was pinned. It read something to the effect of, "This is the beginning of the revolution," Second Assistant Sheriff Kevin McMahill told reporters.
"We don't necessarily believe that they are white supremacists or associated with the Nazi movement. We believe that they equate government and law enforcement ... with Nazis," McMahill said. "In other words, they believe that law enforcement is the oppressor."
"I just sat down to have lunch. The officers were sitting in front of me, at the table right next to me, and this man came in out of nowhere," witness Sheree Burns told CNN affiliate KTNV.
"I thought he was going to get a drink, the way he walked up and walked past them," she said. "And then he turned around, pulled a gun on his right and shot the bald officer in front of me."
The pair took the officers' guns and ammunition, McMahill told reporters.
As the Millers walked out of the CiCi's, they passed Alvaro Lopez.
"They had a backpack, and I saw a gun in their hand," Lopez told CNN affiliate KLAS. "He just told me to tell the cops that it was a revolution and that he'd just killed two cops inside CiCi's."
McMahill confirmed that the Millers said something about a revolution while leaving the pizzeria.
A search for why
Police are still in the early stages of their investigation. They say they think that the couple acted alone and that the officers shot were targeted at random, authorities said Monday.
"What precipitated this event, we do not know," Sheriff Doug Gillespie said. "My officers were simply having lunch."
Investigators searched an apartment late Sunday night that was thought to be where the couple lived. They were going through the couple's social media postings, McMahill said Monday.
Police also recovered hundreds of rounds of ammunition from the couple's backpacks at Walmart, suggesting they were prepared for a lengthy gunbattle, he added.
"There is no doubt that the suspects have some apparent ideology that's along the lines of militia and white supremacists," McMahill said.
A woman who says she lived near the couple told KTNV that the married couple liked to dress up as the villainous "Batman" characters Joker and Harley Quinn.
The neighbor, Krista Koch, told the station the man also sometimes dressed as Slenderman, a fictional horror character that recently surfaced in the stabbing of a 12-year-old girl in Wisconsin.
Koch also told the station the couple had told her they were going to carry out an attack, but she thought they were "crazy," so she dismissed what they said.
McMahill told reporters he'd heard unconfirmed reports the pair spoke to a neighbor about the attack before it happened.
"You know we have the 'see something, say something' campaign," he said, urging people to call police when something doesn't feel right.
"We need to hear about those times when individuals or groups of individuals are talking about going out and committing acts of violence -- whether it's against the police or anybody else in our community," McMahill said.
"We need to hear from our citizens. They're the best eyes and ears that we have out there."
CNN's Jack Hannah, Stephanie Elam and Kyung Lah reported from Las Vegas; CNN's Shimon Prokupecz, Matthew Stucker and Janet DiGiacomo contributed to this report.