Details are sketchy but sources within the Las Vegas Metropolitan Police Department say the officers were shot by a man and a woman who approached them as they ate lunch at a CiCi's Pizza, 309 N. Nellis Boulevard, at about 11:20 a.m.
Sheriff Doug Gillespie identified the officers as Alyn Beck, 42, and Igor Soldo, 32. He said no motive for the attack has been determined.
"It's a tragic day," the sheriff said. "We have lost two officers with young families."
There are still many questions whose answers won't be known immeidately, Gillespie said.
A law enforcement official who has been briefed on the incident said one officer was refilling a soft-drink when the female shooter approached him from behind and shot him in the head, killing him instantly.
The woman then shot the other officer several times as he was trying to draw his pistol. Initial reports indicate that Soldo was the officer shot at the soda machine, but that has not been confirmed. :Gillespie did say one of the officers was able to fire back.
One officer was reportedly dead at the scene, while the other died later in surgery at University Medical Center. Both were uniform patrol officers assigned to the Northeast Area Command. Beck was a senior patrol officer who had taught Advanced Officer Skills Training and at the Metro academy.
Witnesses told police one of the shooters yelled "This is the start of a revolution" before shooting the officers. Gillespie later said he could not confirm the shooters said that.
The shooters then stripped the officers of their weapons and ammunition and went into the Walmart across the street at 201 North Nellis.
Witnesses at the scene reported hearing shots fired in quick succession inside the Walmart.
At a news conference at about 1 p.m. Assistant Sheriff Kevin McMahill said the male shooter, described as a tall white man, yelled "everyone get out" before shooting.
One unconfirmed report is that the two exchanged gunfire with a citizen who was carrying a concealed weapon, and that one of the shooters was injured.
Gillespie confirmed someone, whose name has not yet been released, was shot and killed just inside the front doors of the Walmart.
As Metro officers entered the front and back doors of the store they exchanged gunfire with the shooters, Gillespie said.
The female shooter then shot and wounded her accomplice before shooting herself in the head, a law enforcement official said. The man then shot and killed himself. Their identities have not been released by police.
Both shooters were reportedly carrying large duffle bags, and a bomb squad was called to the scene. It's unclear at this time what, if anything, was found in the bags. A fire department official said the bomb squad response was "a precaution."
The FBI was called out to the shooting.
Metro asked for any available off-duty officers to work Sunday afternoon. Patrol squads were doubling up so each officer would have a partner, sources said. Metro officers usually patrol solo, but Gillespie said they would continue to ride with partners in the coming days while the investigation continues.
Metro also asked all department members to shroud their badges with a diagonal black band, which is often done as a sign of respect for fallen officers.
"It's a very, very difficult day," Gillespie said, "but we still have a community to police, and we still have a community to protect."
Marlene Buck works at the Denny's on Nellis across from WalMart. She said she was impressed with how quickly Metro responded.
"It took less than fifteen minutes," she said.
As squad cars cordoned off the street, Buck said restaurant customers crowded against the windows and started to rush outside.
"I did everything I could to keep everyone inside," she said, adding it looked like a warzone and making a machine-gun gesture with her hands.
Late into the afternoon dozens of bystanders were standing outside police tape, watching the investigation. Walmart employees and shoppers cried and hugged before police took them to be interviewed in a nearby store. After talking with witnesses, officers took them to one of several buses waiting in the parking lot.
A grandmother who was shopping in Walmart with her two teenage granddaughters said they crouched in a makeup aisle when they heard shots. She prayed out loud, but the girls asked her to keep quiet so the shooters wouldn't find them. When they peeked around the aisle and couldn't see the shooters, they ran out of the store.
Cici's and Walmart were closed while Metro investigated. CiCi's Vice President of Operations Geoff Goodman expressed condolences on behalf of the chain.
"We are deeply saddened by this tragic event and our hearts go out to the families and friends of the officers," Goodman said in a statement. "CiCi's is assisting police in any way we can."
Metro had never before seen two officers killed in a single incident. Gillespie said Sunday was an "unprecedented day."
Three Las Vegas police officers have died in separate on-duty incidents in recent years.
David Vanbuskirk, who died during a helicopter rescue at Mount Charleston, was the first Metro officer killed on-duty since 2009, a year when three officers died in traffic crashes and officer Trevor Nettleton was shot.
Nettleton had just finished his patrol shift when he was attacked in his garage by several would-be robbers, who were later charged with his murder. Although Nettleton had finished his patrol shift and was in street clothes, Metro classified his death as on-duty.
Sgt. Henry Prendes was shot and killed responding to a domestic violence call in 2007.
"We have been luckier than other police agencies," a Metro officer who asked not to be identified said Sunday. "In a town like this, with the criminals and scumbags we're dealing with every day, you're always wondering when something is going to happen."
The agency lists 18 other on-duty deaths in department history, including seven officers killed before the Las Vegas Police Department consolidated with the Clark County Sheriff's Office in 1973.
Las Vegas Mayor Carolyn G. Goodman called the attack "a senseless and cruel act killing three innocent people, two who dedicated their lives to protecting all of us in our community and one who was innocently going about her daily life. At UMC Trauma and thereafter with fellow officers, I saw their pain was evident and clear. Their resolve was greater than ever to serve our community with loyalty, dedication and to honor the memory of their two comrades and friends."
Goodman directed that all flags at city facilities be lowered to half staff.
Gov. Brian Sandoval late Sunday issued the following statement about the attack:
"I am devastated by the news today of two officers and an innocent bystander who were murdered in an act of senseless violence. My thoughts and prayers go out to the victims and their families. I am receiving regular updates with regard to this tragedy and local and state law enforcement are assisting at the scene."
Gillespie said he had spoken with the families of the fallen officers.
"Of course, they're devastated," Gillespie said. "At a moment's notice they've lost their loved one. But we will be very close by and we will work very closely with them as we move forward through the grieving process."