The twin who survived a suicide pact with her sister refuses to provide police with any information on why the shooting took place.
Candice Hermeler suffered a head injury and her sister Kristin died instantly when they shot themselves at a range near Denver, Colorado.
The 29-year-old twins were Australians who had been travelling on cultural exchange visas, and one had been scheduled to return home the next day.
"The surviving sister has confirmed that they had planned to commit suicide together, and did in fact shoot themselves," Captain Louie Perea told the Herald Sun.
He said that, although police had asked about why it happened more than once “the victim did not want to answer that question, so we have abandoned that question.”
The women had been in the area about five weeks and had visited the shooting range twice before, taking lessons during one visit.
They chatted casually with other shooters after arriving at the range on the day of the tragedy.
A 15-year-old scout was the first to notice when the sisters fell down, and he shouted "There's a problem, there's a problem!" to his father Bill Gwaltney, a shooting instructor.
The tragedy marked at least the seventh suicide involving rented guns at US shooting ranges this year, and the third at the Family Shooting Centre since 2004.
Police searched luggage the sisters had left at a hotel and found articles about the 1999 Columbine High School killings, mobile phones, $US120 and a notebook, which contained no information on what they did at the shooting range.