DENVER (Reuters) - Authorities are trying to unravel the mysterious double shooting of twin sisters from Australia at a Colorado gun range which left one woman dead and the other in critical condition.

The simultaneous shootings of the 29-year-old sisters occurred on Monday at the Family Shooting Center in suburban Denver, Captain Louie Perea of the Arapahoe County Sheriff’s Office said on Wednesday.

Perea said no third party was involved, but until the investigation is complete, detectives “won’t make a judgment” as to whether the shootings were an attempted double suicide, a possible murder-suicide or a tragic accident.

The women rented handguns at the range and were target shooting in side-by-side stalls for about 90 minutes before the incident. A surveillance videotape showed the two women fall backward but did not capture the actual shooting, Perea said.

One twin died at the scene and the survivor was in critical but stable condition with a head wound.

“She underwent surgery, and so we have been unable to interview her,” Perea said.

Because of their similar appearances, it was unknown which sister died and which survived, so authorities have not released their names. Perea said relatives may be able to aid in the identifications, but if not the coroner will rely on fingerprints or dental records.

Family members were en route to Colorado from Australia and were expected to arrive sometime on Wednesday, he said.

Police said the twins were from the southeastern Australian state of Victoria. The family was notified through the Australian consulate’s office in Los Angeles.

Perea said the two women were in the United States on cultural-exchange visas, with one woman arriving in August and the other in September. The pair were staying at a nearby motel and took a taxicab to the shooting range, he added.