Unable to talk, Sierra found the strength to make a simple hand movement to confirm who had shot her.
It was her 15-year-old stepbrother Levi Elliott, reported UK's The Daily Mail.
The incident took place on March, 2012.
He was found guilty of fatally shooting his sister and was sentenced to 30 years in prison last month, reported US newspaper The Springfield News-Leader.
Levi, 17, received a 20-year sentence for second-degree murder, a five-year sentence for armed criminal action and a five-year sentence for tampering with a motor vehicle.
Sierra lived in a rural area of Missouri with her mum, step-dad and his biological son, Levi,
While she was popular and well-liked by her school mates, Levi told his school friends he hated his stepsister.
"I wouldn't care if she died," he had said.
On March, 2012, Levi and Sierra were left alone for under an hour.
She was watching television in the master bedroom when Levi came in and shot his stepsister in the head.
He then drove away, leaving her to bleed to death.
He stopped at a pay-phone where he called his biological mum and stepfather, telling them an intruder had burst into their home and shot Sierra.
Despite not having a licence, he drove all the way to their home in Kansas City.
When Peggy and James came home, they found Levi gone and Sierra dying on their bed, they asked her whether it was Levi who had shot her, she raised her hand to signal yes. She died from her injuries the following day.
The same day, Levi surrendered to the police and stuck with his story about an intruder, but he was convicted by a jury last October for shooting his sister.
This article was first published on Feb 3, 2015.
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