Possible Clues:

• Disinterested in right and wrong
• Scent sent back by student without scruples?
• Unacquainted with ethics
• Like the stranger in Camus's 'The Stranger'
• Lacking values
• With no ethical standards
• Unprincipled to spread alarm about nothing
• By the end of the morning it's bad, in a manner of speaking
• With no concern for right or wrong, Miss Marple's all but last following up scent
• Morning examination is unethical