Two Las Vegas police officers and a civilian were killed in an apparent ambush that ended with the two gunmen dying by suicide.
One of the attackers yelled "This is the start of a revolution" before shooting the officers and stripping them of their weapons and ammunition.
Two officers were shot by the gunmen, a man and a woman, as they ate lunch at CiCi's Pizza.
One of the officers died at the scene, while the second subsequently died in surgery.
The attackers then headed to a nearby Walmart store, exchanging gunfire with and ultimately killing a civilian who was carrying a concealed weapon.
The shooter, described as a tall white man, yelled "everyone get out" before shooting Assistant Sheriff Kevin McMahill.
The two gunmen then went to the back of the Walmart for "some kind of suicide pact." Mr McMahill said.
Earlier, police alerted the public on their Twitter feed saying that they were investigating a multiple shooting at the 300 block of N Nellis.
The tweet said "Persons have been injured. Avoid the area. Please RT. #Vegas.
We're investigating a multiple shooting at the 300 block of N Nellis. Persons have been injured. Avoid the area. Please RT. #Vegas— LVMPD (@LVMPD) June 8, 2014