ST. CLOUD — Authorities have arrested an 18-year-old St. Cloud man who they said fatally shot his 16-year-old sister.

The teen was being held in the Mille Lacs County Jail on Tuesday on probable cause for second-degree murder. The county sheriff’s office said deputies responded to reports of a shooting death inside a parked RV at the Rum River State Forest in Mudgett Township on Friday night.

Deputies said the teen shot his sister during a fight in the RV while they were camping.

The Anoka County Medical Examiner’s Office will conduct an autopsy on the girl.