The court's refusal to review the case means in turn that the previous court's sentencing will stand. Both teenagers were sentenced to 20 months in a juvenile detention facility for the murder.
The 15-year-old girl was found beaten and strangled in the Stockholm suburb of Stureby in June last year. The 16-year-old boy later confessed to killing her, but the girl denied having anything to do with the murder.
But SMS messages featured in the trial showed in part how the girl encouraged her then boyfriend to kill the teenager after he admitted to kissing her.