According to the Southern Poverty Law Center (SPLC), the alleged Wisconsin Sikh shooter had roots in the white power music community.
This is a brief diary. According to this link, Wade Michael Page had roots in the white power music scene. Obviously, if this is the same individual (which may or may not be the case), then this would be a compelling, if tragic explanation for yesterday's awful events.
For those who've never seen it, this is a link to David Neiwert's interactive map of right-wing violence since 2008.