Mass killings, like Friday's schoolhouse slaughter in Connecticut, have become a troubling and recurring fact of life in the United States.
Other recent mass shootings include:
* August 2012: An Army veteran kills five men and a woman at a Sikh temple in Wisconsin.
* July 2012: A student opens fire at a midnight showing of the latest Batman movie at a Colorado theater, killing 12.
* January 2011: U.S. Representative Gabrielle Giffords and 18 other people are shot outside a supermarket in Arizona.
* November 2009: An Army psychiatrist kills 13 soldiers and civilians on the Fort Hood Army base in Texas.
* April 2007: A students kills 32 people on the campus of a large university, Virginia Tech.
* April 1999: Two students at a Colorado high school kill 12 classmates and a teacher.
The Mother Jones magazine says that since 1982, there have been at least 61 mass murders in the U.S., which U.S. authorities define as an assault in which a gunman kills four or more people, typically in a single location.