massacre versus tragedy

i was watching world news tonight and there was a story on school shootings. the story refered to the columbine shootings as the "columbine masssacre." this took me back to my high school days when i went to a school about a half an hour away from columbine high school when those shootings happened. on the local news the shootings were referred to a "tragedy," however in national reports it was called a "massacre." it may just be my narrow perspective, but when violence happens in a certain area, the locals convey the incidents as "tragedies" rather than use harsher words such as "massacre." i wonder what's the difference? is there a difference or is just semantics?