LOS ANGELES (AFP) - A gun-toting couple who killed two US cops in cold blood saw police as oppressors and may have had anti-government militia links, officials said Monday, recounting the chilling execution-style attack.

In the third mass shooting in three weeks in the western US, the couple placed a swastika symbol at the scene of the cop killings before going on to shoot dead a civilian at a nearby Walmart and then killing themselves.

Jerad and Amanda Miller apparently had views "along the lines" of white supremacists, although police do not believe they were themselves white supremacists, said assistant sheriff Kevin McMahill.

Jerad Miller pinned a note to one of the bodies stating: "This is the beginning of the revolution," after killing them in cold blood at a pizza restaurant where the officers were having lunch.

The couple entered the restaurant Sunday, walked past the booth where the officers were eating, and then Jerad Miller "pulled a handgun out and shot officer (Igor) Soldo one time in the back of his head," said McMahill.

"Officer Soldo immediately succumbed to his injuries. At that time, officer (Alyn) Beck immediately began to react, when he was confronted by lethal gunfire from Jerad Miller, and he was shot once in the throat area," he told reporters.

The couple then both shot multiple rounds into the two officers, before pulling their bodies out of the restaurant booth.

They placed an American revolutionary flag on one of the bodies, "and also threw a swastika on top of his body." Jerad Miller then "pinned a note to officer Soldo basically stating that this is the beginning of the revolution."

Officers were still investigating the motive for the attack, but McMahill said, "there's no doubt that the suspects have some apparent ideology that's along the lines of militant and white supremacists." However, he added, "we believe at this point, with the swastika, 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 ... and those who support it with Nazis.... They believe that law enforcement is the oppressor." The couple eventually holed up in the back of the Walmart store, where Amanda Miller shot her husband before taking her own life.

Police were investigating links to Cliven Bundy, a Nevada cattle rancher who billed himself as a people's hero, who was locked in a showdown with US federal authorities earlier this year.

Bundy also became the unlikely ring-leader of a spontaneous armed right-wing militia, who sprang to his defense to prevent federal police from removing his cattle.

Jerad Miller said on his Facebook page that he was at the Bundy ranch, further north in Nevada, during the cattle standoff. "We continue to utilize investigative resources to determine if in fact that is true," said McMahill.

The Vegas shooting is the third in only a few weeks in the former Wild West region of the United States. On May 23, a student with mental problems, the son of a Hollywood director, went on a gun rampage at a college campus in Santa Barbara, north of Los Angeles, killing six people and then himself.

On June 5, a gunman killed one person and injured two others on on a college campus in the northwestern US city of Seattle, in what the local mayor denounced as America's "epidemic of gun violence". School shootings have become a periodic tragic occurrence in the United States in recent years.

They include the December 2012 massacre in Newtown, Connecticut that left 20 small children dead, and the Virginia Tech shooting in April 2007 in which 33 died, including the gunman.