The decision about whether a teenager charged with killing her sister last year should be tried as an adult or a juvenile is now in the hands of a Lancaster County judge.Prosecutors and attorneys for Claire Miller delivered closing arguments Wednesday afternoon, following two and a half days of testimony.The defense summed up why Miller, now 16, should be tried as a juvenile, while the prosecution said Miller wanted to commit murder for months and should spend time in prison.Assistant District Attorney Amy Muller told the judge Miller was "a kid who had it all but was obsessed with homicide." Muller cited thousands of text messages Miller sent a friend expressing a desire to harm someone.Muller said Miller loved her sister, Helen, "but she was an easy target. She couldn't fight back." Helen Miller had cerebral palsy.Defense attorney Bob Beyer countered that Claire Miller "suffered a psychotic first break" and didn't mean to harm the sister she loved."Even our best and brightest children have demons. We need to deal with them," Beyer said.Miller was 14 on Feb. 22, 2021, when Manheim Township police said they found her covered in blood outside her home. She allegedly told officers she had stabbed her 19-year-old sister to death.On Monday, Miller's parents testified that they had lost one daughter and don't want to lose their other daughter to prison.Doctors called to the stand testified Miller could be rehabilitated, but prosecutors argued she would be a danger to society if she's released from the juvenile rehabilitation system in five years.Judge David Workman is expected to announce his decision July 18.