Section 334

When any person dies while in the custody of the police or in a psychiatric hospital or prison, the officer who had the custody of that person or was in charge of that psychiatric hospital or prison, as the case may be, shall immediately give intimation of such death to the nearest Magistrate, and the Magistrate or some other Magistrate shall, in the case of a death in the custody of the police, and in other cases may, if he thinks expedient, hold an inquiry into the cause of death.

Criminal Procedure Code 185