ENGLEWOOD, Colo. -- The double-shooting of Australian twin sisters that left one of the women dead was a suicide pact, investigators said Thursday after interviewing the surviving sister.
The 29-year-old sisters had been in the Denver area for about five weeks before they went to a shooting range Monday.
Investigators say each woman shot herself in the head with ammunition bought at the range, one using a rented .22-caliber revolver and the other a rented .22-caliber semiautomatic handgun.
The surviving sister remains hospitalized in serious condition. She told officials the two planned to commit suicide together and that they shot themselves at the range, Arapahoe County Sheriff's Capt. Louie Perea said Thursday.
Physical evidence and surveillance video from the range supports that claim, he said.
"She was angry, upset, frustrated -- any of the range of emotions one must feel," Perea said of the surviving sister. "But she still allowed us to complete an interview."
She wouldn't say why the two wanted to commit suicide, Perea said.
Authorities are withholding the sisters' names until they can confirm their identities, and are waiting for copies of the women's fingerprints from immigration officials.
Investigators originally didn't know which twin died and which one survived because they looked so much alike.
No suicide note was found, and investigators have said a search of the twins' luggage at a nearby hotel revealed nothing.
The women, who are from Victoria state in southeast Australia, had been at the shooting center at Cherry Creek State Park before. Perea said one sister underwent gun training two weeks before the shooting. Both showed up at the range about a week later for additional gun training.
It's not clear what the women were doing in the United States. Their relatives are set to arrive in Colorado on Friday afternoon, Perea said.
Both sisters arrived at the Family Shooting Center at about 1:30 p.m. Monday and rented the handguns and bought ammunition.
Shooters at the range stand in wooden stalls and shoot at targets through an opening that resembles a window.
The twins shared a stall and complained to range staff about the noise coming from a patron next to them, who was using a high-powered rifle, Perea said. The sisters were then moved several firing lanes down, away from other shooters.
"I don't know if they did that to be in a more secluded area or what," Perea said.
It was cold, and one of the sisters borrowed a jacket from another patron. Surveillance video shows the sister leaving the stall and placing the borrowed jacket on a table before walking back to her shooting lane, Perea said.
A short time later, surveillance video captured the suicide and suicide attempt. It showed the sisters falling out of the stall about a half-second apart, with other patrons quickly reacting, Perea said.
The twins had been at the range about an hour and 20 minutes.