Abstract: The casing serving as a safeguard against burglary for tape recording cassette containers is made of a plastic material and includes in the narrow wall opposite of the insertion opening a perforation of the wall close to an edge and extending at its center substantially at the level of the angularly adjacent inner surface of the casing into the casing. Two locking bodies arranged adjacent of each other and integrally connected by a base disk and having a hook-like broadened and thereafter wedge-like sharpened end section are inserted into the perforation. The hinged lid of the tape recorder cassette container is kept somewhat depressed by the hook-like broadened end section which end section simultaneously engages over the adjacent side wall of the contained wherewith the container of the cassette and the casing are interlocked. In order to unlock the connection the interconnection between the locking bodies and the base disk resting against the outside of the casing is ruptured by means of a special tool.