BIRU MAHATO vs DISTRICT MAGISTRATE, DHANBAD.

The Supreme Court held that under Section 3(2) of the National Security Act, 1980, preventive detention is impermissible if the detenu's liberty is already curtailed by imprisonment. The Court emphasized that the detaining authority must be aware of the detenu's existing detention, as a lack of awareness vitiates the detention order due to non-application of mind. The appeal was allowed, and the detention order was quashed, establishing that preventive detention cannot be used to further detain an individual already in custody.