On Monday, police were alerted by a neighbor who heard "the sounds of a child" coming from a van parked in the village of Hagenbach, near the borders with Switzerland and Germany, according to a statement from prosecutor Nicolas Heitz released on Saturday.
After forcing open the van, police found the child "in a fetal position, naked, covered with a blanket, on a pile of trash and near excrement," the statement said. The boy was visibly malnourished and could no longer walk because he had been in a seated position for too long, it added.
The boy's father told investigators he had placed his son in the van in November 2024 "to protect him," because his partner wanted to send the child to a psychiatric hospital, the prosecutor stated. The boy was seven years old at the time.
The prosecutor said there is no medical documentation indicating the boy had psychiatric issues before he disappeared and that he had good grades in school.
The boy told investigators he had "great difficulties" with his father's partner and believed his father "had no choice" but to lock him up, according to the prosecutor. He also said he had not showered since 2024.
The father faces preliminary charges of kidnapping and other criminal acts and is being held in custody. His partner denied knowing the boy was in the van, the prosecutor said. Preliminary charges have been filed against her, including for failing to assist a minor in danger, and she has been released under judicial supervision.
The boy's 12-year-old sister and the 10-year-old daughter of his father's partner have been placed in the care of social services.
The prosecution is investigating whether other people knew the boy was being held locked up. Friends and family members told investigators they thought the boy was in a psychiatric institution. His teachers were told he had transferred to another school, the prosecution stated.
Authorities have not released the names of the victim or family members.
Villagers interviewed by the AP agency on Saturday expressed shock at what happened and said they did not know where the boy was, but did not wish to go into details.
The prosecutor declined to comment further on the case to AP, citing the ongoing investigation.