Another riddle

The science teacher at Jefferson High School is murdered on the first day of the academic year. The police narrow down the suspects to four members of the school – the gardener, the coach, the math teacher, and the principal. However, they all have alibis:

The gardener says he was trimming the bushes
 The coach says he was playing basketball
The math teacher says he was conducting a mid-year test
The principal says he was in a meeting 
The police had no trouble in arresting the person guilty of the crime. Who do you think was the murderer?

Is there another riddle than murdering

The principal! It was the first day of school how can he conduct a mid-year test? 

Math teacher, no mid year test in first day of school =)

Oops I meant the math tecaher

Ok. It's math teacher