Authorities credit a Northglenn high school student with alerting them Monday to an Arizona teen's Snapchat hoax about shooting up his school. Police in Phoenix say the Northglenn student alerted a school resource officer to Snapchats that showed students in a hallway with the caption "planning the school shooting" and "in the office again." "The conversation led investigators to Sierra Linda High School (Arizona) where the student was identified," Phoenix police said in a news release. The 16-year-old Arizona student admitted he sent the Snapchats and told officers it was a prank.