The youngster, who has just come of age, was suspected of inhumane treatment leading to death, grievous bodily harm and sexual assault.
Priscilla Sergeant's family are unhappy with this punishment.
14-year-old Priscilla Sergeant was found dead in a field in Dworp (Flemish Brabant) in July 2012. Three suspects were soon held including two minors. The three had abused the girl in the adult suspect's home for several hours before dumping her body.
The 46-year-old adult suspect was arrested, but later freed due to procedural error. The two minors, aged 12 and 16 at the time, were placed in youth detention centres. The case has been dragging on for many years. A police physician came to the conclusion that Priscilla probably died of asphyxia. The investigation was concluded in June 2016.
Prosecutors took into account that the events happened quite some time ago. Suspect J put his life back on track after the events in Dworp and he was forced to stay at a youth detention centre.
Priscilla's family are said to be aware that there are few alternatives in this case, but it is hard for them to accept that somebody who was involved in their daughter's death gets away with a reprimand.