Authorities are trying to determine how twin sisters from Australia were both shot in the head at a Colorado shooting range _ and which sister died and which is critically injured.

The 29-year-old women were shot at an outdoor shooting range at Cherry Creek State Park south of Denver on Monday. Arapahoe County Sheriff's Capt. Louie Perea said Tuesday their family has been notified, but their names haven't been released because investigators don't know which sister died.

"They look very similar," Perea said.

Investigators haven't been able to talk to the survivor, who is in critical but stable condition in an area hospital.

The coroner is trying to identify the sister who died through fingerprints and dental records, Perea said.

Investigators are trying to determine how both women were shot in the head. They aren't looking for any suspects. They're trying to sort out whether the shootings were accidental or intentional.

"Everything's on the table," Perea said.

No suicide note was found, he added.

The women were in the United States on cultural exchange visas. The U.S. Immigration and Customs Enforcement said one of the women was due to leave Tuesday, according to Perea.

It wasn't clear when the other woman was set to return home.

Australia's Department of Foreign Affairs and Trade said in a statement that the twins were from Victoria state in southeast Australia.

Perea said investigators aren't sure who fired the gun or guns, or whether the same bullet hit both sisters, who were in the same shooting lane. The sisters had taken a taxi to the range and had been there for more than an hour when they were shot.

The sisters had a small-caliber weapon at one of the lanes where shooters line up behind a wooden wall and shoot through an opening that resembles a window, Perea said. There was no apparent indication of a dispute between the sisters or anybody entering or leaving the area.

Surveillance cameras captured patrons' reactions to the shooting, but not the shooting itself. A patron notified range officials of the shooting.

Range owner Doug Hamilton told The Denver Post that the women showed no outward signs of trouble or duress when they arrived at the shooting range.

The range was open Tuesday.