Bonus question: Was there any final decision on the motive of the Columbine shooters?

This question is outside the scope of this subreddit. Everyone should keep their answers focussed on the main question, about school shootings more than 20 years ago.

School shootings were definitely occurring in the early 1900's, but it was in the 1990's people were becoming more aware of what was happening seeing as infamous shootings, such as Paducah, Jonesboro, and Columbine. There is an extensive list you can find on Wikipedia of all the shootings that have happened throughout history.

Most experts believe that it was based on some psychopathic urge to kill because their initial plan was to have the bombs go off and kill everyone in the cafeteria, then shoot the remaining survivors as they fled the school.