It cer­tainly lends some evi­dence of prior plan­ning and at least a fas­ci­na­tion with these kind of inci­dents, if not using it as a way to sort of develop a plan,” said Jack McDe­vitt, asso­ciate dean in the School of Crim­i­nology and Crim­inal Jus­tice at North­eastern University.

Other killers have been found with mate­rials from ear­lier mass shoot­ings or cited the crimes, said Jack Levin, a pro­fessor at North­eastern Uni­ver­sity who has written a number of books on mass murderers.

What it indi­cates to me is that he had mass murder in his mind and he was looking for some role models and he quite easily found them in the pub­licity that had been given to other cases,” Levin said.

The mas­sacre at Columbine High School in 1999 has been cited by later killers in the United States and other coun­tries, he said.

The copycat phe­nom­enon thrives on exces­sive pub­licity and we have con­tributed a great deal by dis­playing exces­sively these hor­rific crimes in our pop­ular cul­ture,” Levin said. “The copycat phe­nom­enon doesn’t cause the event to happen. It deter­mines the timing and the method.”

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