A heavily armed shooter entered the Navy Yard in Washington on Monday and opened fire, killing at least 12 people before being shot to death by authorities.
The killings brought the horror of mass shootings back into the national spotlight, as President Barack Obama condemned the "cowardly act" and honored the victims during an address.
Monday's violence marked the sixth mass shooting since the one in Newtown, Conn., in December, according to some counts. It was also the first publicly recognized by Obama since the elementary school massacre, which claimed the lives of 27, including 20 children.
There have been six mass shootings over the past nine months -- and at least 20 during Obama's presidency. That may be disturbing. But some would argue even that startling figure grossly underreports the number of shooting sprees.
The growing number of mass killings over the past five years left the country in search of a term that would distinguish mass murder by gun from those using other weapons. Mass shooting has gained favor as the obvious choice. Though the FBI doesn't specifically define mass shooting, it does define mass murder, calling it a single incident in which a perpetrator kills four or more people, not including himself or herself.
The FBI defined mass murder to distinguish it from serial murder. That definition provides the basis for the unofficial definition of mass shooting that has gained use in recent years. Mother Jones explained the definition in an extensive "Guide to Mass Shootings in America," writing that mass shootings typically involve a single episode in a single location, usually a public place. The Mother Jones definition of mass shooting matches the FBI definition of mass murder in that it includes single incidents that kill at least four victims.
Over on Reddit, the Guns Are Cool community has compiled a list of every mass shooting in the United States this year. The moderators of the subreddit, which doesn't actually appear to be of the belief that guns are cool, use an expanded definition of mass shooting, listing every event in which "four or more people [including the shooter] are shot in a spree." Under the Reddit definition, a shooting spree that wounds at least four people, but doesn't kill them, is still a mass shooting.
Including Monday's mass shooting, the Reddit list for 2013 is nearing 250 incidents. That's an average of one mass shooting almost every day.
With so many mass shootings, even those that fit the frequently used definition rarely prompt a presidential response. Perhaps it's not surprising that many of the violent acts cataloged by Reddit escape national attention.
Below, the 20-plus mass shootings that have made waves on a national scale during Obama's presidency, including the few that have been mentioned by the president himself.
Sept. 16, 2013 -- Washington -- At least 12 dead (including gunman)
A man identified as Aaron Alexis, 34, opened fire at the Navy Yard on Monday, gunning down at least 12 before being killed by authorities.
Obama addressed the incident in a live address later in the day.
"So we are confronting yet another mass shooting and today it happened on a military installation in our nation's capital," he said.
Speaking of the victims, he added: "These are men and women who were going to work, doing their job, protecting all of us. They are patriots and they know the dangers of serving abroad, but today they faced unimaginable violence that they wouldn’t have expected here at home."
July 26, 2013 -- Hialeah, Fla. -- 7 dead (including gunman)
Shooter Pedro Vargas killed six neighbors in a rampage after setting fire to his apartment complex. He was later shot and killed by police.
(No public comments from the president.)
June 7, 2013 -- Santa Monica, Calif. -- 6 dead (including gunman)
Shooter John Zawahri killed his father and brother before going on a shooting spree on and around the campus of Santa Monica College that claimed the lives of four more and injured others.
(No public comments from the president, though he was in the area for a fundraiser.)
April 24, 2013 -- Manchester, Ill. -- 5 dead
A shooter rocked the small town of Manchester when he killed five, including two children, at a federal housing complex. The gunman later died of gunshot wounds sustained during a shootout with police.
(No public comments from the president.)
April 21, 2013 -- Federal Way, Wash. -- 5 dead (including gunman)
After shooting and killing his girlfriend, a gunman gunned down three more neighbors in an apparent attempt to eliminate all witnesses. He was later killed by police.
(No public comments from the president.)
March 13, 2013 -- Herkimer County, N.Y. -- 5 dead (including gunman), one FBI K-9 dead
Kurt Myers, 64, shot six people, killing four, before holing up in an abandoned building. He later killed an FBI K-9 officer during a shootout in which he was eventually killed.
Dec. 14, 2012 -- Newtown, Conn. -- 27 dead (including gunman)
The shooting at Sandy Hook Elementary was the second-deadliest school shooting in U.S. history, leaving 27 dead -- including 20 young children.
President Obama gave an emotional address, calling for "meaningful action":
As a country we have been through this too many times. Whether it is an elementary school in Newtown, or a shopping mall in Oregon, or a temple in Wisconsin, or a movie theater in Aurora, or a street corner in Chicago -- these neighborhoods are our neighborhoods, and these children are our children. We're going to have to come together to meaningful action on this, regardless of the politics.
Sept. 27, 2012 -- Minneapolis, Minn. -- 7 dead (including gunman), 2 injured
Andrew John Engeldinger, a recently laid off employee of Accent Signage Systems, entered the office building and opened fire.
(No public comments from the president.)
Aug. 5, 2012 -- Oak Creek, Wis. -- 7 dead (including gunman), 4 injured
White supremacist Wade Michael Page entered a Sikh Temple, opening fire on congregants. He later shot and injured a police officer responding to the scene.
Michelle and I were deeply saddened to learn of the shooting that tragically took so many lives in Wisconsin. At this difficult time, the people of Oak Creek must know that the American people have them in our thoughts and prayers, and our hearts go out to the families and friends of those who were killed and wounded.
My Administration will provide whatever support is necessary to the officials who are responding to this tragic shooting and moving forward with an investigation. As we mourn this loss which took place at a house of worship, we are reminded how much our country has been enriched by Sikhs, who are a part of our broader American family.
July 20, 2012 -- Aurora, Colo. -- 12 dead, 59 injured
During a midnight screening of "The Dark Knight Rises," a gunman opened fire on the suburban Denver movie theater, killing 12 and injuring dozens of others.
Two days later, Obama delivered a ten-minute speech from the University of Colorado that made no mention of gun control:
God bless all who helped to respond to this tragedy. And I hope that over the next several days, next several weeks, and next several months, we all reflect on how we can do something about some of the senseless violence that ends up marring this country, but also reflect on all the wonderful people who make this the greatest country on Earth.
May 31, 2012 -- Seattle, Wash. -- 6 dead (including gunman)
A man opened fire in a cafe, fatally wounding four people, then killed another in a carjacking before killing himself.
(No public comments from the president.)
April 2, 2012 -- Oakland, Calif. -- 7 dead
A former student of Oikos University, a Korean college, entered a building on the campus and shot repeatedly at random targets.
(No public comments from the president)
Feb. 22, 2012 -- Norcross, Ga. -- 5 dead (including gunman)
A man shot and killed two of his sisters and their husbands and then himself in a Korean health spa.
(No public comments from the president.)
Oct. 12, 2011 -- Seal Beach, Calif. -- 8 dead, 1 injured
Scott Evans Dekraai, 41, stormed a hair salon where his ex-wife worked and killed eight people.
(No public comments from the president.)
Jan. 8, 2011 -- Tucson, Ariz. -- 6 dead, 14 injured
Jared Lee Loughner, 22, opened fire in a Safeway parking lot, killing six people and injuring others including U.S. Rep. Gabrielle Giffords, who was shot in the head at point-blank range.
Two months later, Obama addressed gun control issues in an op-ed for the Arizona Daily Star:
I know that every time we try to talk about guns, it can reinforce stark divides. People shout at one another, which makes it impossible to listen. We mire ourselves in stalemate, which makes it impossible to get to where we need to go as a country. However, I believe that if common sense prevails, we can get beyond wedge issues and stale political debates to find a sensible, intelligent way to make the United States of America a safer, stronger place.
Aug. 3, 2010 -- Manchester, Conn. -- 9 dead (including gunman), 2 injured
A driver for Hartford Distributors killed eight people and then himself in this workplace shooting.
(No public comments from the president.)
Nov. 29, 2009 -- Parkland, Wash. -- 5 dead (including gunman)
A Washington man walked into a coffee shop and shot four police officers execution-style.
(No public comments from the president.)
Nov. 5, 2009 -- Fort Hood, Texas -- 13 dead, 30 injured (including gunman)
In the deadliest shooting to ever happen on an American military base, an Army Major serving as a psychiatrist went on a shooting spree that killed 13.
Obama said at a press conference:
This morning I met with FBI Director Mueller and the relevant agencies to discuss their ongoing investigation into what caused one individual to turn his gun on fellow servicemen and women. We don't know all of the answers yet, and I would caution against jumping to conclusions until we have all of the facts.
April 3, 2009 -- Binghamton, N.Y. -- 14 dead (including gunman), 4 injured
Jiverly Wong, a naturalized immigrant from Vietnam, gunned down students and employees at the American Civic Association, where he had been taking English lessons.
President Obama said in a statement:
Michelle and I were shocked and deeply saddened to learn about the act of senseless violence in Binghamton, N.Y. today. Our thoughts and prayers go out to the victims, their families and the people of Binghamton. We don't yet know all the facts, but my administration is actively monitoring the situation, and the vice president is in touch with Governor Paterson and local officials to track developments.
March 10, 2009 -- Geneva County, Ala. -- 11 dead (including gunman), 6 injured
A 28-year-old man killed his mother then drove ten miles to kill several members of his extended family, neighbors and a bystander. The victims ranged in age from 18 months to 74 years old.
(No public comments from the president.)
March 29, 2009 -- Carthage, N.C. -- 8 dead, 3 injured (including gunman)
A gunman opened fire on a nursing home, killing seven residents and a nurse.
(No public comments from the president.)
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