Thousands of high school students in two US states returned to classes after 48 hours of uncertainty from baseless claims of potential violence on their campuses.Several threats to schools in California's heavily populated San Gabriel Valley, .
The call — which warned of a shooter at Boulder High School — came via the University of Colorado Boulder’s non-emergency dispatch line at 8:33 a.m. on Wednesday.
The Michigan State shooting continues to show the challenges in securing so-called soft targets public places like schools that aren't heavily defended, experts say.