Police say the 29-year-old women had been at the busy Family Shooting Center in Cherry Creek State Park, south of Denver, for nearly 90 minutes, firing rented pistols and chatting. Then, a security video shows, they fell backward nearly simultaneously, hitting the floor outside the shooting stall.
Both had been shot in the head. One died instantly. The other is listed in critical condition at a nearby hospital, hooked to a respirator and unable to speak. Police have not identified them and can't tell which one survived because they look identical, according to U.S., British and Australian media reports.
"Every time I get new information there's a new twist," sheriff's Capt. Louie Perea told the Denver Post. "We're keeping an open mind." Investigators have ruled out the possibility that a third person could have shot them, he said, but have yet to make a final determination. Employees at the firing range said the incident appeared to be a double suicide attempt.
The sisters, who were in the U.S. on cultural exchange visas, had visited the range before, knew how to fire weapons and appeared to be in perfectly normal spirits when they arrived Monday afternoon, investigators said.
"They were interacting with each other, and nothing seemed unusual," Perea said. "They were just a couple of gals having fun at the range."
Mitch Hamilton, one of the center's range officers, said it was impossible to tell from the video if the women shot themselves or each other, according to Australia's Sydney Morning Herald. But it was apparent the bullets did not come from a ricochet or a third source.
The wounds "were self-inflicted. That's what it appears, that's as far we can tell,'' Hamilton said.
U.S. Immigration and Customs Enforcement said one of the women was due to leave Tuesday, according to Perea, Britain's Daily Mail reported. It wasn't clear when the other sister was scheduled to return home. One had arrived in August and the other in September.
It was not known why they were in Colorado. They had been staying at a motel about five miles away and arrived at the range Monday in a cab. The taxi driver told investigators he noticed nothing unusual about the pair, police said.