The girl is from Södermanland and was taken into custody by police at the end of August.
It is true that this girl has had contact with, or that there has been communication between, her and the perpetrator in Fagersta, prosecutor Adolf Moberg Oleszkiewicz tells Ekot.
The crime is classified as preparation for murder, but the prosecutor does not want to say exactly what the suspicion is. The girl denies the crime.
The police have also taken into custody a 13-year-old boy from Gothenburg who had contact with the suspected Fagersta murderer. The boy is suspected of making a serious unlawful threat.
A 16-year-old has previously been detained for aiding and abetting murder and attempted murder.
