In Nevada, a student opened fire at Sparks Middle School Monday, killing a math teacher and wounding two fellow students. The unidentified shooter then killed himself. Police said the teacher, Michael Landsberry, was trying to protect students. The news came the same day Attorney General Eric Holder said the average number of mass shootings in the United States has tripled since 2009. Speaking to a conference of police chiefs, Holder said the United States saw an average of five “active shooter incidents” every year between 2000 and 2008, compared to at least 12 so far this year.