In between, the nation debated gun control -- ultimately Congress sat pat while numerous states loosened their restrictions on gun ownership -- and the carnage went on.
Through the year, there were many mass shootings -- four or more deaths in a single incident as defined by the FBI -- with the Sept. 16 shooting at the Navy Yard in Washington topping the list: Aaron Alexis went on a rampage that left 12 people dead and several more injured before he was killed by police. The massacre tied for 11th on a list of Top 25 mass shootings since 1965.
Handfuls of people died in other shootings: six victims plus the gunman in a Hialeah, Fla., shooting; five victims plus the shooter in Santa Monica, Calif., and Manchester, Ill.; and five dead in Seattle, Albuquerque, Fernley, Nev., and Herkimer, N.Y.
There was a long list of shootings in which four people died, led by Christopher Dorner, a former Los Angeles police officer who killed four people, including three police officers, and wounded three other officers before being hunted down and killed in a stand-off in the San Bernardino Mountains.
And as the deaths piled up across the country, punctuated by the year's worst incident taking place in the nation's capital, U.S. Attorney General Eric Holder, in an interview with CNN, criticized Congress for failing to pass stricter background checks for firearms purchases.
"Yes, we've failed," he said. "It can't be the new normal. It cannot be something that we accept."
But in fact, it is the norm and it's not new. Slate magazine reported recently Northeastern University criminologists James Alan Fox and Monica J. DeLateur, citing FBI figures, say there have been about 20 mass shootings a year since 1976, and "the facts clearly say that there has been no increase in mass shootings and certainly no epidemic." A USA Today analysis of FBI data found that with 2013 winding down, 137 people died in 30 mass killings this year, part of more than 900 people killed in the past six years.
"Everyone is always asking 'Why are these mass killings increasing?''' Fox told the newspaper. "They are not.''
Mass shootings are a small percentage of the tens of thousands killed by firearms each year in the United States, and an even smaller fraction of the number wounded. For example, a burst of gunfire in a Chicago park in September left 13 people, including a 3-year-old boy, injured, though no one died.
GunsAreCool on Reddit.com keeps a running list of mass shootings at http://www.reddit.com/r/GunsAreCool/wiki/2013massshootings.
PsychCentral.com reported Fox and DeLateur point out there are no easy solutions to ending gun violence, noting for example there is no proven causal link between violent entertainment such as video games and mass murder, no telltale signs to tip off authorities to likely mass killers and mental health facilities may not reach mentally unstable people outside the mainstream before they resort to homicidal mayhem.
"Taking a nibble out of the risk of mass murder, however small, would still be a worthy goal for the nation," they said.
"However ... eliminating the risk of mass murder would involve extreme steps that we are unable or unwilling to take -- abolishing the Second Amendment, achieving full employment, restoring our sense of community and rounding up anyone who looks or acts at all suspicious.
"Mass murder just may be a price we must pay for living in a society where personal freedom is so highly valued."
Here are some of the worst cases of U.S. mass killings in 2013:
-- Jan. 19, police say Albuquerque teenager Nehemiah Griego used an assault rifle and a .22-caliber rifle to kill his father, a pastor, and four other family members. The youth was charged with five counts of first-degree murder. A police statement said Nehemiah told investigators he was angry with his mother the night of the slayings and he had anger issues as well as having homicidal and suicidal thoughts.
-- March 13, police say Kurt Myers, 64, described as a loner, shot four men to death and wounded two others in a barbershop and service station before being killed at the end of a 19-hour standoff with police in Herkimer, N.Y.
-- April 22, law enforcement officials said Dennis Clark III, 28, shot and killed his girlfriend and three innocent bystanders in Seattle before being killed by police.
-- April 24, investigators say Rick Smith, 43, of Roodhouse, Ill., involved in a custody battle, apparently broke into a house in Manchester, Ill., and killed five members of a family, then carried a 6-year-old girl to a neighbor's house before fleeing. He later was killed in an exchange of gunfire with police.
-- May 13, admitted gang member Jeremiah Diaz Bean, 25, allegedly fatally shot five people, including an 84-year-old couple, in and around Fernley, Nev. He also was suspected of burglary and arson.
-- June 7, a 2-year-old California man, John Zawhri, 23, used an assault rifle, possibly assembled himself to circumvent gun laws, in a shooting spree that started at his father's house and ended at Santa Monica College and six people fatally shot before police ended his life.
-- July 26, police say 42-year-old Pedro Vargas burned $10,000 in cash in his apartment to lure apartment complex managers Italo and Camira Pisciotti. He fatally shot them and four others before police killed him and freed two hostages.