On Sunday morning, as Igor Soldo and Alyn Beck were eating lunch in a CiCi’s Pizza not far from the Las Vegas Strip, Jerad Miller walked into the restaurant. Miller turned around, walked outside and returned a moment later with Amanda, his wife. Soldo and Beck, two officers with the Las Vegas Metropolitan Police Department, were sitting in a booth when the Millers walked over and opened fire.

Jerad Miller shot Soldo, 31, once in the back of the head, police said the following day. He then shot Beck, 41, in the throat, after which both Millers fired at Beck multiple times. Authorities said the entire episode was captured by the surveillance camera inside the restaurant. The couple placed a yellow “Don’t Tread On Me” Gadsden flag and a swastika on Beck’s body before pinning a note to Soldo’s body that read “This is the beginning of the revolution,” according to Kevin C. McMahill, assistant sheriff of Clark County.

Following this, the Millers picked up their backpacks and moved south along Nellis Boulevard to a nearby Wal-Mart. Jerad Miller fired one round into the air, telling the shoppers to leave because a revolution was beginning and the police were coming, McMahill said. A shopper named Joseph Wilcox, 31, was near the registers when this happened. Wilcox, who was carrying a concealed weapon, told a friend he was going to confront the suspects. But as Wilcox headed over to Jerad Miller, he walked by Amanda Miller, who shot him once and killed him, police said. As two police teams arrived, drawn by the 911 calls from both locations, the Millers and the police began exchanging gunfire. By the time the Millers made their way to the back of the store, both were wounded. Amanda Miller took her own life, and while authorities initially thought she shot and killed her husband first, they said later that he died from wounds sustained during the firefight.

The following day, as details began to emerge about the background of the couple, a portrait started to take shape. They “have an ideology that’s along the lines of militia and white supremacists,” McMahill said at a news conference Monday. This anti-government view included a belief that law enforcement “is the oppressor,” he said. A neighbor of the couple told the Los Angeles Times that Jerad Miller had talked about killing police officers. The couple had left a considerable trail online suggesting a deep hatred of the government.

Earlier this year, when an armed group of supporters joined rancher Cliven Bundy in his standoff with federal agents, the Millers went to the ranch to join them. “I feel sorry for any federal agents that want to come in here and try to push us around or anything like that,” Miller told Al Jazeera America at the time. “I really don’t want violence toward them, but if they’re gonna come bring violence to us, if that’s the language they want to speak, we’ll learn it.” One of Bundy’s sons told the Associated Press the Millers were asked to leave the ranch for conduct reasons and called the couple “very radical.”

Authorities investigating the shootings have said they are not linking the violence to the Bundy ranch visit. McMahill, choosing his words very carefully during a news conference, pointed out that a lot of people with various ideologies gathered at the ranch. “But as you well know, in the hundreds of people who were at the Bundy ranch, these are the only two who went from ideology to action,” he said.

There is still much we do not know about the shootings in Las Vegas. The “massive, ongoing investigation,” as McMahill called it, entails going through considerable video and physical evidence and interviewing many people to try and figure out the why of the whole episode. Clark County Sheriff Douglas C. Gillespie said police believe the couple was acting alone. The Las Vegas police are the lead agency investigating the shootings, while the FBI is working closely with the police as well as other law enforcement agencies, FBI spokeswoman Bridget Pappas said.

Police have said there was additional information on the note left on Soldo’s body, but they are not releasing those details yet. Authorities also found other material relating to the couple and are reviewing it in order to figure out the thought process leading up to the killings.

“Because an individual may espouse an ideology [online] that is anti-government or anti-police, that doesn’t mean they will translate into a murderer,” McMahill said. “What happened to change these people into murderers, we don’t know and we are working diligently to find out.”

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The bloodshed in a restaurant and a store is the latest in a series of violent sprees that have recently erupted in our schoolscollegesshopping mallsmovie theaters and beachfront towns. But the attack on two uniformed police officers, and the particular anti-government and anti-police sentiments expressed by the shooters, evoke warnings that have come from authorities in recent years. The FBI has referred to individuals who believe that governments in the United States operate illegally as “a growing domestic threat to law enforcement.” In September 2012, Michael Clancy, deputy assistant director of the FBI’s counterterrorism division, warned that extremists could carry out “smaller, localized acts of violence” and some could target law enforcement and government officials.

An assessment issued by the Department of Homeland Security in April 2009 discussed the potential threat posed by “domestic extremists.” As an example of the potential violence associated with such extremists, it cited the incident earlier that year where a gunman shot and killed three police officers in Pittsburgh. (The assessment, which said that factors including the economic downturn and the election of President Obama “may be invigorating rightwing extremist activity,” was savaged by conservatives and Republican lawmakers. Many people were particularly critical of the report’s warning that returning veterans having trouble readjusting could pose a threat. Groups called for the ouster of Janet Napolitano, the secretary of homeland security at the time, and she issued an apology.)

There is a movement that believes that the federal government has dangerously overstepped its authority, and within that movement are groups that believe they need to be ready to fight back against any perceived overreach, said J.M. Berger, a terrorism analyst.

In 2012, the Southern Poverty Law Center issued a report on what it called a “stunning” rise in the number of groups it had identified as part of the overall movement. The report said it tracked 1,274 such groups in 2011, up from 824 the year before.

Many of these people “are not going to be violent,” Berger said. “It’s not like this is a group of thousands of potential terrorists here. But they do have a view on things that is definitely outside the mainstream. And they have a focus on preparation for armed resistance that is very problematic.”

A report issued last year by the Combating Terrorism Center at West Point warned that when people who believe the federal government is their enemy turn violent, they “direct most [of] their violence against the federal government and its proxies in law enforcement.”

It is unclear if the danger from such people is on the rise. Federal officials said they haven’t seen any movement when it comes to the threat from anti-government extremists. “There is no uptick or specific threats at this time,” one high-ranking law enforcement official told The Post.

Another official said these groups have posed a longstanding threat, but echoed what experts said in noting that many of the anti-government people or groups never turn to violence or do anything illegal.

“Anti-government extremist groups have been a consistent threat for years and they pose a significant challenge to law enforcement,” James M. Trusty, head of the Justice Department’s organized crime and gang section, said in a statement. “Many of these groups spout hatred, but never cross the line into criminal activity.”

It can be difficult to determine a real threat because “someone may be on the radar for decades before they take a step toward violently enforcing their views,” he said.

But experts do say there appears to be an increasing danger for police and other people in law enforcement.

“My sense is there is a rising threat to law enforcement officials,” said Mark Potok of the Southern Poverty Law Center. “We’ve seen quite a number of cases that either target law enforcement officials or see police as the enemy.”

The Las Vegas incident came two days after a gunman seeking to take hostages shot a sheriff’s deputy in Cumming, Ga., about an hour north of Atlanta. Authorities said they haven’t found evidence that the gunman, who had had numerous encounters with law enforcement, was part of any anti-government groups.

There may not be a rise in anti-law enforcement sentiment, said David Gomez, a former FBI agent and Los Angeles police officer. He pointed out times that the Weather Underground took credit for or was blamed for bombing police stations.

“From the time I was a police officer, we were always aware of…people wanting to kill police officers because they’re police officers,” he said. “They’ve always been out there.”

Rather, it’s possible that we’re simply hearing about more of these incidents because of the modern nature of the media, Gomez said.

Still, when people who see the federal government as the enemy turn violent, police are endangered because they are a uniformed group that can be easily found and can represent the government, said Jim Johnson, Baltimore County’s police chief and chairman of the National Law Enforcement Partnership to Prevent Gun Violence.

“This is a real threat,” Johnson said. “We all live with this…Anyone in the public safety system I think is at greater risk from individuals who are anti-government.”

Over the last decade, there has been an added focus on training officers in how to deal with this increasing danger, Johnson said. The National Law Enforcement Partnership to Prevent Gun Violence, an organization comprised of law enforcement leadership organizations, said that ambushes of police officers has increased recently.

There were 82 officers shot and killed in 2012 and 2013, and 22 of those deaths occurred in ambush-related shootings, according to the National Law Enforcement Officers Memorial Fund.

In the wake of the Las Vegas shooting, Gillespie, the Clark County sheriff, said he thought the danger of being targeted was likely on the minds of his officers.

“Is that weighing? Sure,” he said Monday. “It would be naive on my part to think that isn’t weighing heavy on their minds as they’re out.”

* * *

The violence against these police officers, and the notion that such a threat could be growing, also brings up another question that emerged after the Las Vegas violence: Was it terrorism? It wasn’t identified as such in media reports covering the shooting.

This question isn’t easy to answer, in part because, as the FBI puts it, “there is no single, universally accepted, definition of terrorism.” The federal code defines terrorism as “the unlawful use of force and violence against persons or property to intimidate or coerce a government, the civilian population, or any segment thereof, in furtherance of political or social objectives.” But the lack of an agreed-upon definition means different events can be classified in different ways, which can make them register differently in the public consciousness.

“What I think is true generally of the media across the board is that people are perfectly willing to call ‘foreigners’ who are attacking us in some way terrorists,” Mark Potok said. “There seems to be a great reluctance to use that label with American citizens, even when it’s obviously called for.”

There are times the term is openly used to describe Americans acting on the U.S. soil. For example, authorities as well as news organizations — including The Post — called Timothy McVeigh a terrorist in covering the Oklahoma City bombing. Other cases are less agreed upon. Why, for example, was the shooting rampage in Santa Barbara, Calif., which involved a gunman who explicitly said he was going to target women, not a terrorist act?

“One of the problems with an inconsistent definition of terrorism is basically, if a Muslim does it it’s terrorism and if a white guy does it, it’s not,” J.M. Berger said. “If the guy in Santa Barbara said Jews instead of women and said ‘Allahu Akbar’ in his video, it would be called terrorism.”

Berger’s comments were echoed in a statement by a spokesman for the Council on American-Islamic Relations.

That lack of a definition is a problem, Berger said, because we need to know what the term means so we know what kinds of problems we’re talking about.

The FBI deferred questions about whether the shooting could be classified as terrorism to the Las Vegas police, who did not respond to a query seeking comment.

Still, the issue is clear to some experts in the field. Gomez, the retired FBI agent who has worked extensively on domestic terrorism, said that the shooting in Las Vegas was clearly terrorism. The shooters targeted police officers and spoke about revolution, suggesting that it was a political action, he said.

“In the generally accepted definition of terrorism, terrorism is an event that targets innocent civilians,” he said. “Some people may argue the police were not innocent civilians, but the manner in which they were attacked, they were not a threat.”

But this killing was about what the officers represented, Gomez said.

“They represented society, they represented the government,” he said. “The point is to send a message to the government that you are incapable of protecting your people.”

By comparison, Gomez said the shootings in Santa Barbara weren’t terrorism because there was no political act or attempt to attack the government. Still, the entire debate is “an academic argument,” he said.

“It doesn’t matter to law enforcement,” Gomez said. “What you’ve got is a triple homicide in Las Vegas.”

Sari Horwitz contributed to this report.