The latest U.S. mass shooting  has turned attention again to the issue of gun control. This is a timeline of events since the Newton, Conn., massacre last year:

Dec. 14, 2012

26 people — including 20 children aged six and seven — were shot and killed at Sandy Hook Elementary School in Newtown, Conn. The gunman's mother was also found dead at her home. The gunman, Adam Lanza, 20, committed suicide at the school. He used a legally purchased high-powered rifle in the shooting.

Dec. 16, 2012

U.S. President Barack Obama, who had been in office during shootings at Fort Hood, Texas, Aurora, Colo., and Tucson, Ariz., but who had largely remained quiet on the gun-control issue, told a Newtown vigil that he would use the power of his office to engage citizens and officials in the coming weeks to help prevent further tragedies.

"We can’t tolerate this anymore. These tragedies must end. And to end them, we must change," said Obama.

Dec. 19, 2012

Obama taps Vice-President Joe Biden to lead a task force on preventing gun violence. The president set a late January deadline for the group's recommendations, which he pledged to act on swiftly.

Jan. 11, 2013

The leading gun advocacy group in the United States, the National Rifle Association, rejects Obama's proposals for a ban on sales of assault weapons, limits on high-capacity ammunition magazines and universal background checks for gun buyers. The NRA pushes for armed guards in all schools.

March 13, 2013

Kurt Myers, 64, of Herkimer County, N.Y., shoots four people in two towns before he is killed by police following a nearly 19-hour standoff.    

April 17, 2013

Despite a bipartisan deal on some parts of the proposed gun-control legislation, it was ultimately defeated in the Senate. The legislation failed to get the 60 votes needed and all Obama's major initiatives, including the background checks, were defeated.

April 21, 2013

Dennis Clark III, 27, of Federal Way, Wash., kills his girlfriend at their apartment, another two people in the parking lot of the building, and then one more person in another building. He is killed by police.    

June 7, 2013

John Zawahri, 23, of Santa Monica, Calif., kills his brother and father at home before he heads to Santa Monica College. He is eventually shot and killed by police.

July 26, 2013

Pedro Vargas, 42, sets fire to his apartment in Hialeah, Fla., and shoots and kills six people in the building before police shoot him.

Sept. 16, 2013

12 people are killed and three others injured in a shooting at the Washington Navy Yard. The alleged gunman, Aaron Alexis, 34, is killed in shootout with police.

Said California Democrat Senator Dianne Feinstein, a leading gun control proponent, in the wake of the attack:  "This is one more event to add to the litany of massacres that occur when a deranged person or grievance killer is able to obtain multiple weapons  including a military-style assault rifle  and kill many people in a short amount of time."