Finding out the correct sentence:I don't know why did he leave early, I need not to know why he left early,I should know why was he leaving early, I don't know why he left early.
Finding out the correct sentence:I don't know why did he leave early, I need not to know why he left early,I should know why was he leaving early, I don't know why he left early.
Explanation
This sentence is grammatically correct: "I need not to know why he left early".