I just output the wiki lists it appeared you were working from. Once you start selectively editing you open yourself up to acts of cherry picking so I didn't edit anything. It's possible that I missed string entries that didn't follow a sort on the date column, I'll take a look again later but here is my list for us school spree shootings this century:
Lanza 27 Goh 7 Kazmierczak 5 Cho 32 Roberts 5 Weise 9 Total 85