Who Killed the Professor

"Who Killed Professor Applewood age 65 and why?  He was about to retire from teaching Biochemistry at the Two River's Academy for boys.  A boarding school for teens grades 8 to 12.  A small private school with only the brightest teens and a few not so bright but had parents with lots of money and some not so rich.  Money that got their not so bright son's in the best private school in the state.  What they paid in Tuition, Room and Board allowed a few less then wealthy students scholarships based on their grades.  Now you might think there are a few wealthy brats at the Two Rivers Academy.  The trouble makers.  You might be wrong.  Would a student have killed the Professor?  Was it one of the faculty members.  There is Professor Templeton age 65 ready to retire, he teaches Literature subjects and Grammer.  There is Professor Varga, 45, who teaches Biology subjects.  Then there is Professor Smith, Headmaster age 50 who teaches History subjects and Computer Science.  Professor Delmont age 35 the Professor who teaches Geography subjects.
Let's not forget Mr. Sherman, age 28 our youngest teacher who teaches the Health class, gym, a Clinical Licensed Social Worker, math and is the school nurse.  The Cook Jones, the Security officer Markley, Janitor Stevens.  One of these could have killed Professor Arnold Pie Applewood.  God forbid it was a student.