LA VISTA, Neb. (AP) — The FBI has joined the search for an autistic 11-year-old boy missing since Monday, when he walked out of his elementary school during classes.

Ryan Larsen has been missing since he walked out of his elementary school in La Vista, which lies just southwest of Omaha.

Police say the child has a history of hiding from his family and authorities.

La Vista Police Chief Bob Lausten says police have had to find the boy at least half-a-dozen times, but that he’s never been missing for days at a time.

Lausten also noted that Ryan has been without his seizure medication since he’s been missing.