"Murder in the house"

Mr. Shikdar was stabbed to death in his own bed, while his wife was preparing bed tea for him. The old couple were loved and respected by their near and dear ones. Neither there was a robbery nor a foul play but a well-planned cold-blooded murder. The spare key of the house was with Baabli Ghosh, their tenant, a school teacher, a part-time detective and the prime suspect of the murder.