Twin women from Victoria were shot in the head at an outdoor shooting range in Colorado; one died, the other was critically injured.
Arapahoe County officials have not released the identities of the victims, and Sheriff's Captain Louie Perea declined to name the sisters' home town or release other information until their family was notified.
The women, aged 29, had taken a taxi to the shooting range at Cherry Creek State Park, south of Denver, on Monday.
The local sheriff's office said their visas showed one of them had arrived in Colorado on September 7 and the other on August 19, with one due to fly back to Australia today.
They had been at the Family Shooting Centre for more than an hour when they were shot.
The incident was partly caught on security cameras, which allegedly show the two women hitting the ground.
Mitch Hamilton, a worker at the centre, said it was impossible to tell from the video if the women shot themselves or each other.
But he said the wounds were not caused by other shooters or a ricocheted bullet.
"[The wounds] were self-inflicted. That's what it appears, that's as far we can tell," he said.
"The video tape shows them simultaneously falling to the ground.
"The police are done with their investigation [at the ranch] because they are not treating it as a homicide."
Mr Hamilton said the twins were chatting and not doing anything unusual leading up to the shooting.
"They were out there shooting for a good hour-and-a-half," he said. "They seemed perfectly normal."
He said the range might typically have about 20 people shooting. They were monitored at all times by two range officers.
Mr Hamilton said he was not there when the shooting happened but it had left staff upset.
"[The range officers] are out there monitoring safety rules constantly," he said.
"In a situation like this there's really nothing they can do. It's pretty rough. It's terrible. It's a sad day at the range."
The owner of the range, Doug Hamilton, told The Denver Post the women were shot nearly simultaneously.
The Post reports the women bought ammunition at the range and spent about 90 minutes firing small-calibre hand guns, even chatting between rounds.
Mr Hamilton said the women showed no signs of stress when they arrived or during their stay.
"The ladies hit the pavement virtually at the same time," he said.
"They were definitely normal.
"We are always aware and watching for signs. There was absolutely no indication."
Captain Perea said investigators were not sure who fired the gun or guns, or whether the same bullet hit both sisters.
The women were in the same shooting lane. In the lanes, shooters line up behind a wooden wall and fire through an opening that resembles a window.
Captain Perea said it was unclear whether the surviving sister would recover sufficiently to be able to provide information.
"We're looking at the last several days she was alive, see where they were and we want to confirm some facts," Captain Perea said.
There was no apparent indication of a dispute between the sisters or anybody entering or leaving the area.
DFAT confirmed the twins involved in the shooting were from Victoria.
"The Department of Foreign Affairs and Trade can confirm that 29-year-old twins from Victoria were involved in a shooting incident at a driving range in Denver," DFAT said in a statement.
"One of the women has died as a result of a gunshot wound. Her sister is currently in serious but stable condition in a Colorado hospital.
"Consular officials from the Australian consulate general in Los Angeles are liaising closely with local authorities.
"The department is providing consular assistance to the women's family in Australia."
AP, Reid Sexton and smh.com.au
