People murdering each other is nothing new, obviously not. The murder rates in the US go down everywhere, and that is the same in the entire industrialized world. The fact is, human beings are getting less violent year after year, and compared to our past selves, we are essentially angels now.
While it could not have literally happened 50 years ago, a similar teacher by student murder could easily have happened. The victim and the perpetrator could have existed. The murder weapon could have existed, as could all the other crime specifics. The difference is the news media. We may not have ever heard about it 50 years ago unless it had been a local story.