At least 49 people were killed and another 53 injured when Omar Mateen, a 29-year-old who worked for a security firm, opened fire at Pulse, a gay nightclub in Orlando, Florida, early Sunday morning. The rampage, which ended with Mateen dead, is the deadliest mass shooting in U.S. history.

Mateen stormed the club armed with an AR-15-style assault rifle and a handgun around 2 a.m., according to the FBI. The New York Times, citing law enforcement officials, reports that Marteen shot about one-third of the 300 patrons that had packed the club for a “Latin flavor” event. The cavernous club quickly became a scene of chaos, as terrified people poured out onto the street, some carrying wounded and bleeding victims. The Times adds that the initial attack was followed by a three-hour standoff, with people held hostage until 5 a.m. That’s when law enforcement agencies raided the club with armored vehicles. Mateen was killed after a gunfight broke out with police.

The FBI is investigating the attack as an act of domestic terrorism. Around the time of the shooting, Mateen, an American citizen whose parents were from Afghanistan, called 911 and pledged allegiance to the Islamic State, federal officials said.

Mateen’s father said his son was driven by homophobia. In an interview with NBC News, he said Mateen became distressed after witnessing two men kiss in Miami two months ago.

“This has nothing to do with religion,” Mir Siddique said. “They were kissing each other and touching each other and he said, ‘Look at that. In front of my son they are doing that.’”

On Sunday, President Barack Obama, who called the rampage a hate crime, addressed the country for the 14th time in the aftermath of a mass shooting. The president said the attack underscores the need for gun reform.

“This massacre is a further reminder of how easy it is for someone to get their hands on a weapon that lets them shoot people in a school or a house of worship or a movie theater or a nightclub,” Obama said. “We have to decide if that’s the kind of country we want to be. To actively do nothing is a decision as well.”

The toll of dead and injured exceeds the 2007 shooting at Virginia Tech, where 32 people were killed, and the 2012 Sandy Hook shooting, where 26 people were killed.

The number of dead also nearly matched the total number of people fatally shot in Orlando in all of last year. At least 51 people were shot and killed in the city in 2015, according to data from the Gun Violence Archive, a nonprofit organization that records U.S. shootings by monitoring media reports and police blotters.

The violence is not normal,” said Vice President Joe Biden in a statement issued Sunday, “and the targeting of our lesbian, gay, bisexual, and transgender Americans is evil and abhorrent.”

Below, four pieces of key context to keep in mind as more details emerge.

The gunman was most likely armed with the kind of high-capacity magazine that some states have banned.

Cellphone camera video footage filmed by a civilian outside the Pulse nightclub recorded at least 20 shots fired in rapid succession in one nine-second stretch. The high rate of fire suggests the shooter used what many jurisdictions call “high-capacity magazines,” a term for ammunition-feeding devices that typically hold more than 10 or 15 rounds.

High-capacity magazines have been used by many mass shooters. Syed Farook and Tashfeen Malik, who gunned down 14 people in San Bernardino, California, in December, used magazines that held 30 rounds each. Jared Loughner used a 33-round magazine to kill six people in the 2011 Tucson, Arizona shooting that injured U.S. Representative Gabrielle Giffords. When James Holmes carried out a shooting at a movie theater in Aurora, Colorado, that same year, he was equipped with magazines that held 40 and 100 rounds. A 2013 analysis by Mother Jones found that half of mass shooters between 1982 and 2012 used magazines that held more than 10 rounds.

The manufacture of high-capacity magazines was outlawed for a decade by the 1994 assault weapons ban. After it lapsed in 2004, some states and municipalities began instituting their own high-capacity magazine bans. Currently, eight states have some kind of restriction on magazine size: California, Colorado, Connecticut, Hawaii, Maryland, Massachusetts, New Jersey, and New York.

Gun rights advocates claim restrictions on magazine size are arbitrarily set and unconstitutional. Gun violence prevention advocates argue that devices that allow users to shoot more bullets before needing to reload results in higher body counts. They point to the example of the Tucson shooting: Loughner was stopped by a bystander when he had to reload.

High-capacity magazine bans have also been challenged as ineffective, as many ordinances apply to the manufacture but not to the possession or sale of the devices. California politicians have been particularly aggressive in trying to close these sorts of loopholes. Last year, Los Angeles banned not just the manufacture but the possession of magazines that hold more than 10 rounds. Gavin Newsom, California’s lieutenant governor, is campaigning to institute a similar rule statewide. He’s been criticized by many pro-gun groups, including one, the Pink Pistols, made up of LGBT shooters.

There’s data to suggest that magazine capacity bans make it harder for criminals to obtain the devices. An analysis by the Washington Post found that during the decade the federal ban was in effect, the number of guns equipped with high-capacity magazines seized from criminals by Virginia police fell by nearly half. When the ban expired, the number of seized guns went back up again.

A large number of hate crimes and domestic terrorist acts are committed with firearms.

The motivation behind the Orlando nightclub attack appears to stem from a confluence of violent homophobia and radical Islamic ideology. While authorities have yet to pinpoint motives, and while it’s difficult to say which form of hatred was the primary motivation, guns are often used in both hate crimes and domestic terrorism.

According to a report on the use of guns in hate crimes released earlier this year by the Center for American Progress, roughly 43,000 hate crimes in the United States were carried out with a gun between 2010 and 2014. Racial bias was the most common motivator for firearm hate crimes, accounting for nearly half of those incidents overall. Bias against sexual orientation and religion was the second-most common motivator.

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Similar trends have emerged in domestic terror attacks, many of which are committed by lone wolf actors, the report found. Nearly 60 percent of domestic terrorist attacks carried out between 2009 and 2015 were carried with a gun, according to the Southern Poverty Law Center.

A report by the Anti-Defamation League examining incidents of fatal domestic terrorism and extremism in 2015 found that 48 of the 52 individuals killed in these incidents were murdered with a gun.

“If you build a bomb, it takes a bit of sophistication and training,” says domestic terrorism expert Daryl Johnson, formerly of the Department of Homeland Security. Since 9/11, “law enforcement has become very adept at identifying the technical signatures of bomb makers.”

The scope of the horror in Orlando is unprecedented. But there is nothing at all unusual about gun violence in Florida.

Last July, 39-year-old Andrew Chisholm and his 17-year-old nephew, Tarvese Johnson, were shot and killed in the breezeway of an apartment in Fort Myers, Florida. Relatives said that Chisholm was the target, and Johnson was caught in the crossfire.

A few weeks later, at 4 a.m. on a weekday morning, three armed men broke through a glass door of a small home across the street from an elementary school in Bradenton, Florida. They shot and killed Kantrel Brooks and Esther Deneus, both 29. Five children under the age of 11 were in the house at the time.

And in Daytona Beach last September, two college students, Timesha Carswell, 21, and Diona McDonald, 19, were shot point-blank in the head by one of their roommates, who they had asked to move out. The shooter, according to news reports, was furious about $200 that he claimed the women owed him. He also gravely wounded a third person in the apartment, forcing him into a closet and shooting him six times through the door.

Chisholm, Johnson, Brooks, Deneus, Carswell, and McDonald were six of the 767 people who were murdered with a gun in Florida in 2015. That averages out to just over two gun deaths a day, or 64 a month. The vast majority of these shootings get scant attention.

The ‘Gunshine State’ has been a testing ground for looser firearms laws.

Over the last three decades, Florida has often served as a laboratory for legislation that expands gun rights, earning it the nickname the “Gunshine State.” Its concealed weapons law, drafted in the late 1980s, has been duplicated by 40 other states, and since 1999, the Florida legislature has passed more than 30 pro-gun bills.

One of those laws, “stand your ground,” was later adopted by 21 other states. During Florida’s last legislative session, there was an attempt to strengthen it even further, making self-defense claims essentially impregnable. That effort failed, along with a push to allow guns on college campuses, and an attempt to give licensed gun owners the right to carry their weapons in public.

Florida has issued 1.4 million concealed carry permits to its residents, far more than any other state in the country. That group included the Orlando shooter, Omar Marteen.

Follow @teamtrace for the latest updates.

[Photo: Loren Elliott/Tampa Bay Times via AP]