on campus. n brks krrk christie smith join where a lot of students decided to stay home. >> reporter: you could really see the difference. there were hardly any students out here walking home. a spokesperson said 20% of the students who actually go here came to school today. today we saw officers stationed over there and the fbi says they are involved because they were asked to be. a show of force by san ramon police, officers drove around the campus of california high school and even walked the halls, all in response to three separate threats of violence in a matter of days. >> there is a lot of people that didn't show up today. >> reporter: this junior showed up knowing police would be here but she was still concerned. >> yesterday someone wrote in a bathroom stall they would shoot up the library and courtyard. >> reporter: kids say there were also racist slurs. police say they have no clear evidence of a credible threat but not taking any chances, even