Thirteen people have died after a former Navy reservist opened fire at a naval base in Washington, D.C., Monday morning, killing 12 people and wounding several others before dying in a shootout with police. The gunman has been identified as Aaron Alexis, a 34-year-old who had been arrested at least twice in the past for shooting-related incidents, but who had security clearance to enter the Washington Navy Yard and worked for a military contractor. Alexis was discharged from the Navy Reserve in 2011 following what officials termed a “pattern of misbehavior.” In 2010, he was arrested in Fort Worth, Texas, when his downstairs neighbor complained he had fired a bullet through his floor into her apartment. In 2004, he was arrested in Seattle after firing his pistol into the tires of a car. At the time, Alexis’ father told police his son had participated in the 9/11 rescue effort and had anger issues possibly tied to post-traumatic stress disorder. Alexis told police 9/11 “had disturbed him.” Alexis did technology-related work for a company called the Experts, a subcontractor to Hewlett-Packard. Officials said he purchased at least one of the guns used in Monday’s rampage legally. He was found with three weapons: a shotgun, a semi-automatic pistol and an AR-15 assault rifle. According to the Associated Press, Alexis was being treated at the VA for multiple disorders, including hearing voices. Eight victims have been identified publicly, all of whom are believed to be civilians or contractors. According to Mother Jones, it is the fifth mass shooting in the United States since the massacre at Sandy Hook Elementary School less than a year ago. President Obama responded to the shooting on Monday.

President Obama: “We are confronting yet another mass shooting. And today it happened on a military installation in our nation’s capital. It’s a shooting that targeted our military and civilian personnel. These are men and women who were going to work, doing their job protecting all of us.”

The D.C. Navy Yard shooting comes just after a major report on gun ownership in the United States confirmed the link between firearm homicide rates and the number of people who own guns. According to the study in the American Journal of Public Health, for each 1 percent increase in gun ownership, the rate of people murdered by firearms increased by 0.9 percent. The researchers found “states with higher rates of gun ownership had disproportionately large numbers of deaths from firearm-related homicides.”

United Nations inspectors say they have found “clear and convincing evidence” that rockets loaded with the nerve agent sarin were deployed in three neighborhoods of the Damascus suburb of Ghouta in a chemical attack on August 21. The report cites medical and environmental evidence, as well as more than 50 interviews with survivors and healthcare workers. It concludes “chemical weapons have been used in the ongoing conflict between the parties in the Syrian Arab Republic, also against civilians, including children, on a relatively large scale.” The report did not assign responsibility for the attack. The United States, Britain and France seized on the findings to bolster claims that only the regime of President Bashar al-Assad could have conducted the attack, while Russia accused them of jumping to conclusions. U.N. Secretary-General Ban Ki-moon spoke to reporters about the report.

U.N. Secretary-General Ban Ki-moon: “The findings are beyond doubt and beyond the pale. This is a war crime and grave violation of the 1925 protocol and other rules of international law, customary international law. It is the most significant confirmed use of chemical weapons against civilians since Saddam Hussein used them in Halabja in 1988 and the worst use of weapons of mass destruction in the 21st century.”

The U.N. inspectors plan to return to Syria to investigate other suspected chemical weapons attacks, including some which the Assad regime claims were perpetrated by rebels.

Turkey says it shot down a Syrian military helicopter that strayed about a mile into its airspace Monday, marking an increase in tensions between the two countries. According to Turkey, the helicopter’s crew failed to heed warnings to turn back.

At least two people are dead and dozens injured after a powerful typhoon hit Japan, damaging thousands of homes and prompting evacuation orders for hundreds of thousands of people. The typhoon complicated clean-up efforts at the embattled Fukushima Daiichi nuclear plant, where workers were forced to dump more than 1,100 tons of rainwater that had pooled around storage tanks holding radioactive water. The plant’s operator said the water’s radiation levels were considered safe. Meanwhile, the death toll from two storms that slammed Mexico from opposite coasts has risen to at least 41 amid some of the worst flooding in decades. And the confirmed death toll from historic floods in Colorado has risen to eight. Scientists have long predicted an uptick in such extreme weather events as a result of human-caused climate change.

A new report has found 50 of the world’s top corporations produce 73 percent of greenhouse gas emissions that fuel global warming. According to the Global 500 Climate Change Report, Wal-Mart and ExxonMobil are among the top 50 polluters whose emissions have risen about 1.7 percent since 2009.

Events are planned in New York City today to mark the second anniversary of Occupy Wall Street. On September 17, 2011, thousands of people marched on the financial district, then formed an encampment in Zuccotti Park, launching a movement that shifted the conversation on economic inequality. At an event Sunday, organizer Justin Wedes reflected on the lasting impact of Occupy Wall Street.

Justin Wedes: “I think it’s exciting, what we’ve seen, in terms of Occupy’s effect both inside and outside of the political system. We talk a lot about the street protests. We talk a lot about the police. And those are important issues. But we’ve also seen the effect of Occupy as high as Congress. We have Senator Elizabeth Warren, who called herself in many ways the 'ideological mother' of Occupy in the most important and influential committee in the Senate, the Senate Banking Committee. You have mayors all across the country who marched with Occupy, who are now standing up for underwater homeowners, like in Richmond, California. You have the foremost frontrunner for the mayor of New York City, Bill de Blasio, the only [major mayoral candidate] who said he would not have shut down Occupy. So I think we’re seeing a new kind of social movement today that’s having an effect within the political system without necessarily entering into it by traditional means.”

Two years after the Occupy movement brought widespread attention to the gap between the richest 1 percent and the 99 percent, that gap is wider than ever. University of California researchers recently revealed 95 percent of income gains since the recession ended have gone to the top 1 percent. On Sunday, ABC’s George Stephanopoulos asked President Obama about that gap.

George Stephanopoulos: “Ninety-five percent of the gains to the top 1 percent, that is so striking.”

President Obama: “It is. And the folks at — in the middle and at the bottom haven’t seen wage or income growth, not just over the last three, four years, but over the last 15 years.”

House lawmakers are set to consider a Republican-backed bill that would cut food stamps by an estimated $4 billion annually and let states impose sweeping new requirements on employment for recipients of food aid. The bill would also allow states to require drug testing food stamp recipients.

The latest document leaks from Edward Snowden show the National Security Agency is targeting international financial transactions involving customers of major credit card companies, including Visa. According to the German magazine Der Spiegel, the NSA’s financial records database, Tracfin, housed 180 million records in 2011. The records included data from a Brussels-based network used by thousands of banks to securely send information on transactions. One document shows the NSA’s British counterpart, GCHQ, expressed concerns about the bulk collection of financial data, which it said contained “rich personal information,” much of it “not about our targets.”

In New York City, Bill de Blasio has cemented his victory in the Democratic primary to run for mayor after second-place challenger Bill Thompson conceded the race and endorsed him Monday. De Blasio ran on a progressive platform to replace outgoing Mayor Michael Bloomberg, criticizing Bloomberg’s support for the police tactic of “stop and frisk” and vowing to take on growing inequality between rich and poor. De Blasio will face Republican candidate Joe Lhota, a former deputy to Mayor Rudy Giuliani, in November.