The search for answers after Monday's tragic shooting at the Washington Navy Yard continues, but for now the Navy is already swiftly moving to bolster its background check system as it appears Aaron Alexis slipped through the cracks. 

Defense Secretary Chuck Hagel and Chairman of the Joint Chiefs of Staff Martin Dempsey announced on Tuesday that there will now be sweeping reviews of Defense Department security clearance protocols. "We will review everything," Hagel told reporters during a briefing, adding "We don't live in a risk-free society. We will find those gaps and we will fix those gaps." Dempsey, in turn, defended the Navy against reports that budget cuts were responsible for security lapses at the Navy Yard that gave the shooter easy access to the complex. "The budget issue did not degrade the security at the Navy Yard and in any way contribute to this," Dempsey said.

On Monday, 34-year-old subcontractor and former Navy reservist Aaron Alexis used his certified access card to enter a building at the D.C. Navy Yard and kill 12 civilians and injure many more, including two law enforcement officials, despite a long history of gun-related arrests and mental health issues. A Defense Department inspector general audit released late Tuesday revealed budget cuts led to lapses in the security clearance process at seven of ten Navy facilities; the report found 52 convicted felons were erroneously granted security clearance. 

But if budget issues were not responsible for Alexis receiving security clearance despite his history, then what was? A bipartisan team of Senators — Democrats Jon Tester and Claire McCaskill and Republicans Ron Johnson and Rob Portman — want to know. They're calling for an independent investigation into how Alexis received clearance. Time's Zeke Miller reports Alexis first received clearance in 2008 when he was still with the Navy, and that clearance was rolled over when he became a subcontractor with The Experts, which contradicts some earlier reports that he passed a second check: 

According to a Pentagon official, records show Alexis was subjected to just one background investigation for his “Secret” clearance in August 2007, which checked national and local law enforcement agencies, as well as his credit history. His clearance was granted in March 2008, when Alexis was a Naval reservist. There is no evidence that Alexis was reinvestigated this year, government sources said, despite some media reports that he was. The Pentagon official said that when Alexis left the Navy and began working for a defense contractor, his clearance was reciprocally accepted, as is standard government policy.

In one final sad development, Alexis's mother broke her silence for the first time since the shooting on Tuesday morning, apologizing to the victims' families. "I'm so, so very sorry this has happened. My heart is broken," Cathleen Alexis said. "His actions have had a profound and everlasting effect on the families of the victims... I don't know why he did what he did, and I will never be able to ask him why."