It must have played some role in the explanation. Finally, is the mystery of evil. I cannot answer this. But we know that sin is the core cause of evil. It would seem logical to conclude that an entire stream of sins connect and link to an explanation of why Eric Harris and Dylan Klebold did what they did in Littleton.
Evil is horrific and offensive.
Harris and Klebod were trapped and enslaved to all forms of evil. There is the center of the issue of causation. You cannot ignore the biblical proposition that their disrespect for life and their rage and hatred for other human beings has its source in the matrix of items I have preciously discussed. There is no simple answer to Littleton. But an understanding of it must begin with human rebellion against God.