No people were hurt, but police said they had no choice but to kill after the agitated animals escaped their enclosure about 10 a.m. and started running through yards and opening car doors in a neighborhood of horse pens, palm trees and tile-roofed, landscaped homes.
Neighborhood resident David Plunkett said he saw the male chimpanzee jump on top of a police car—with its lights on and an officer inside—before the animal jumped to the ground and headed into a vacant lot.
"We tried to establish a perimeter until the experts arrived," said Officer Marcus Martin, a Las Vegas police spokesman. "But at least for the first animal, they couldn't get there in time."
The Las Vegas chimps were on the loose for about 30 minutes with police trying to corral them before a male primate believed to weigh more than 150 pounds was shot and killed. The other chimp, a female, was shot with a tranquilizer dart but continued to roam the area for several more minutes before she was hit with a second dart.
She succumbed in neighbor Tony Paolone's three-acre backyard. Martin said she was returned to her cage shortly after noon.
"They got out, and the police did what they had to do," said Paolone, a paving company worker who was at work during the commotion and was prevented for a time from returning to his house while police investigated afterward.
Paolone, who keeps 12 horses on his property, said he knew the chimps lived behind a home on his street for several years. He said he never saw them loose and he never felt threatened.
Clark County spokesman Dan Kulin said the owner had proper permits to keep the animals on the property in unincorporated county territory outside Las Vegas city limits, as well as a license from the U.S. Department of Agriculture.
Martin said police were called at 10:13 a.m. and officers saw the two chimps ambling through the neighborhood, pounding on cars and climbing at one point into the driver side of an empty black sport utility vehicle and then out the passenger side. A trainer offered the animals food and tried to lure them back into captivity.
Police warned residents through Twitter not to leave their vehicles or homes and to avoid the area where the "dangerous" primates were roaming free. Martin said at least one police car was dented by the animals pounding on it.
A woman called 911 saying a large chimpanzee was on top of her car, Martin said. She told dispatchers she had her windows rolled up and doors locked.
Plunkett, 36, said he was alerted to the commotion by the sound of a helicopter. He estimated the animals to be about 4 feet tall. Adult chimps can be as tall as 5 1/2 feet when standing upright.
Martin said police officers tried to corral the animals to await animal control officials, but the male chimp turned toward the gathering crowd. A veteran officer with a shotgun killed it a little before 10:45 a.m. The officer's name wasn't immediately made public.
Plunkett said he heard three shots. Helicopter video showed the animal lying face down in the middle of a road, surrounded by animal control trucks and police cars.
"We have an exotic animals policy. It's to treat them as humanely as we can," Martin said. "But immediately you recall the woman who has no face because of a chimp. The officer knew they were dangerous animals and he was the last line of defense with citizens behind him."
Martin referred to a 2009 attack on a woman who was permanently blinded and when her nose, lips, eyelids and hands were mauled by a chimp before police killed the animal outside a home in Stamford, Conn.
Two adult chimpanzees also attacked a U.S. student last month after he entered their enclosure at a primate sanctuary in South Africa.