Who is the murderer ?

 It was the time of first day of new year.

It was early in the morning.. 

School children have not yet come to the school. 

But some of teachers had come to school. 

They were History teacher, Mathematics teacher, Basketball coach, gardener and the principal himself. 

One tragic incident happened. 

The history teacher of the school got murdered.

Police have come to school for the interrogation. 

Gardener said He was in the garden working since early morning. 

Mathematics teacher said She was preparing the question paper for mid term exams of the school. 

Basketball coach said He was busy in preparing the basketball court to play. 

Principal said He was busy in doing administrative work. 

Police noted down everything. 

Finally, they have arrested the murderer. 

Guess who ??? 

Murderer is Mathematics teacher   !!!! 

How did police find out ?? 

It was the time of first day of new year.. 

Mathematics teacher said that she was busy in preparing the mid term exam question paper  !!! 

In the beginning of the year, who will prepare the question paper for the mid term exams  ??!!!