A 2015 investigation by CNN identified "more than 40 people...charged with Columbine-style plots." A 2014 investigation by ABC News identified "at least 17 attacks and another 36 alleged plots or serious threats against schools since the assault on Columbine High School that can be tied to the 1999 massacre." Ties identified by ABC News included online research by the perpetrators into the Columbine shooting, clipping news coverage and images of Columbine, explicit statements of admiration of Harris and Klebold, such as writings in journals and on social media, in video posts, and in police interviews, timing planned to an anniversary of Columbine, plans to exceed the Columbine victim counts, and other ties. 60 mass shootings have been carried out, where the perpetrators had made at least a single reference to Harris and Klebold.