First, regardless whether the defendant possessed an FID card, there were sufficient articulable facts to create a reasonable suspicion for the patfrisk and search of the backpack. In the wake of school shootings such as occurred at Columbine, Colorado; Santee, California; and Newtown, Connecticut, "we take judicial notice of the actual and potential violence in ... schools," Commonwealth v. Milo M., 433 Mass. 149, 156 (2001), and note the heightened sensitivity of school officials to signs that a student may have brought guns onto school property and might embark on a shooting rampage. See generally G.S. Katzmann (ed.), Securing Our Children's Future: New Approaches to Juvenile Justice and Youth Violence 1-27, 386-414 (2002). The officer observed the presence of three types of ammunition and a hunting knife openly displayed in the defendant's vehicle, the defendant's aggressive posture, his camouflage attire, and the threatening decals on his vehicle. When taken in combination, these facts justify a frisk of both the defendant's person and backpack because a reasonable person in the officer's position would fear for his own safety and that of others on a college campus. Indeed, the presence of ammunition alone gave rise to a reasonable inference that a firearm was also present. ... Based on the presence of the ammunition and the reasonable inference that a gun might be nearby, it was reasonable for Officer Donovan to suspect that his safety and the safety of others at the college were in danger.