Two sisters were shot in Colorado on Monday. One survived; one didn't. Here's the thing: They were twins, and the police don't know which one is which.

But, okay, let's back up, because this is a pretty mysterious story (courtesy Denver's 9News): Two Australian sisters, twins, both 29, arrive in the U.S. on cultural exchange visas, one in August and one in September. They stay in a hotel in Arapahoe County, Colorado. On the Friday before one twin's Tuesday departure date, they check out. It's still unclear where they go over the weekend, but on Monday they arrive at the Cherry Creek State Park shooting range by taxi, and reserve a lane. They spend an hour and 20 minutes shooting with small caliber guns. And then both are shot.

One dies, and one survives. And—since they're twins—police can't identify which one is which. The surviving one (who was shot in the head) made it through surgery, but police haven't been able to question her, and haven't been able to contact their family.

In fact, authorities haven't said—or maybe won't say—what, exactly, happened at the shooting range. But the 9News story strongly hints that the sisters shot each other: Police "are not currently searching for a suspect"; they "do not believe there was any kind of fight that led up to the shooting"; the shooting is being investigated as a "death" and not a "homicide." The shooting range owner, Doug Hamilton says the shots occurred "nearly simultaneously":

He believes the women were recreational shooters, and said the shooting was not an accident.

"It was a deliberate shooting," Hamilton said.

When asked why, he said, "From what I know of the things I cannot tell you."

Tragic and puzzling all at once, huh? The C.S.I. writers must be salivating over this one.

[9News via BreakingNews; stock photo of twins via Shutterstock]