Obviously we live in a day and age where you can never be too careful. If you see something you should say something. However sometimes the something you see can turn out to be nothing.
Late yesterday (5/1/17) someone believed they saw someone on Colgate University's campus with a gun. They immediately contacted authorities and the campus went into lockdown.
However after investigating the matter they found that there was no gunman. Just someone with glue gun working on an art project.
Here's a statement from the University:
After thorough investigation, and with the assistance of the person in question, law enforcement identified the individual as a student who was using a glue gun for an art project, confirmed the misunderstanding, and released the campus from lockdown.
Better safe than sorry.