Mr. Jayant Prasad was murdered in his bungalow while he was asleep. Except him, his four brothers lived in the house. The coroner could discern only one set of footprints in the bedroom , that supposedly of the murderer! The coroner , by the means of some evidence came to the conclusion that the murderer was one of those who lived in the house! He knew it was useless to question them directly so he asked -
" how did the murderer come in ? "
His brothers A,B,C,D replied as follows:-
A- " through the door "
B- " through the window"
C- "through the door "
D- " I don't know "
Assume that only the culprit would lie and only one of them could be the killer! Who killed Mr. Jayant Prasad?