Rampage motive still a mystery after 14 slain

Teresa Hernandez (right) and Monique Gutierrez hug at the Rudy Hernandez Community Center as they wait for a relative, who was not injured, after the shooting rampage. ALEX GALLARDO/REUTERS

Following the 2012 school shootings in Newtown, Connecticut, which claimed 28 lives, including 20 children, the Obama administration initiated but failed to push stronger gun control laws.

The laws, whose sections included expanded background checks and bans on assault weapons, were stymied in Congress after staunch opposition from Republican lawmakers and gun-rights lobby groups.

During his presidency, Obama has been confronted with more than a dozen of high-profile mass shootings, and in an interview earlier this year he called the failure to reform U.S. gun laws "one of the greatest frustrations" of his presidency.

"If you ask me where has been the one area where I feel that I've been most frustrated and most stymied, it is the fact that the United States of America is the one advanced nation on Earth in which we do not have sufficient common-sense gun safety laws, even in the face of repeated mass killings," Obama told BBC in July.