The top prosecutor for Franklin and Hampshire counties said Tuesday that reports that a retired mathematics teacher at Deerfield Academy, an exclusive prep school in Western Massachusetts, had sexual contact with a student in the 1980s are “deeply disturbing.”

“Deerfield Academy appears to be taking an important first step to independently investigate inappropriate contacts ­between a former teacher, Peter Hindle, and a student,” said a statement issued by Northwestern District Attorney David E. Sullivan.