The shooting at Sandy Hook Elementary School in Newtown, Connecticut, is among the deadliest in modern US history. Since 1999 there's been 6 tragedies just like todays.
The most memorable, the Columbine Shooting in Littleton, Colorado, where 12 people were killed by Eric Harris and Dylan Klebold, among the dead were their classmates and teachers.
On Nov. 5, 2009, thirteen soldiers and civilians were killed and more than two dozen wounded when Army Psychiatrist Nidal Hasan walked into the soldier readiness processing center at Fort Hood, Texas, and opened fire.
On April 16, 2007, Seung-Hui Cho kills 32 people and himself on the Virginia Tech campus in Blacksburg, Virginia.
On July 20, of this year, at least 12 people were killed when James Holmes entered an Aurora, Colorado movie theater, releases a canister of gas and then opened fire during opening night of the Batman movie "The Dark Knight Rises."
Since 1982, there have been at least 61 mass murders carried out with firearms across the country, with the killings unfolding in 30 states from massachusetts to Hawaii.
But the US is not the only country to suffer tragedies:
Last year, a man believed to be a former student shot 10 people dead at a school in Rio de Janeiro, wounded 18 others before taking his own life.