DRIPPING SPRINGS, Texas -

Central Texas police say a couple kept their adopted son locked in a garage apartment for at least four years, periodically giving him a box of food and allowing him to leave once a week.

A police affidavit reveals the apartment behind the Dripping Springs home of 40-year-old Jenifer Elise Thyssen and 39-year-old Dane Andrew Thyssen was locked from the outside. The couple told police 22-year-old Koystya Thyssen was locked in the apartment to protect their other children.

Police began investigating when Koystya Thyssen was arrested for allegedly burglarizing a neighbor's home. Authorities say he used a screwdriver taken from his father to escape the apartment.

The couple were being held Friday at the Hays County jail on a kidnapping charge. The younger man also is being held there, on a burglary charge.