In the early hours of Sunday morning, Omar Mateen opened fire inside a gay nightclub in Orlando. He killed 49 people and injured 53, making it the deadliest mass shooting in U.S. history.
What's perhaps most devastating about the slaughter is how preventable it might have been. Mateen had a history of domestic violence, exhibited signs of mental illness, was once on the federal government's terror watch list (though he was later removed) and used an assault rifle outfitted with a high-capacity magazine.
Here are the kinds of legislation designed to prevent people like Mateen from being able to carry out acts of violence — but that were not in place at the time of his massacre.
1. More and stronger domestic-violence laws
Mateen's ex-wife, Sitora Yusufiy, said the shooter was physically and verbally abusive during the couple's four-month marriage. Her parents "rescued" Yusufiyr from him, she told reporters Sunday. "They had to pull me out of his arms, and buy an emergency flight. I left all of my belongings, we made a police report," she said.
Anti-gun-violence advocates have had decent success passing legislation to keep individuals with a history of domestic violence from getting guns. Last year alone, state legislatures in Alabama, Delaware, Louisiana, Maine, Nevada, Oregon, South Carolina, Vermont and Washington all passed laws limiting or prohibiting abusers' access to guns.
This year, anti-gun groups are working to advance 30 domestic-violence-related bills in not only Florida but also Arizona, Georgia, Hawaii, Kansas, New Jersey, New York, Ohio, South Carolina, Virginia, Vermont and Wisconsin.
Such measures enjoy overwhelming support from the general public: A 2013 poll found the 81 percent of all respondents — including 76 percent of gun owners — supported a the idea of banning gun ownership for a decade after a person is convicted of violating a domestic-violence restraining order. Nearly three-quarters of those polled, both gun owners and non-owners, were in favor of prohibiting gun ownership for ten years after a person is convicted of domestic violence.
2. Provisions to add mentally ill individuals to background-check registries
Yusufiy said that during their time together, Mateen exhibited signs of troubling mental illness: "He was mentally unstable and mentally ill; obviously disturbed, deeply, and traumatized."
While research has shown that the mentally ill are more likely to be victims of violence than perpetrators, legislation that would keep guns out of the hands of mentally ill individuals is one of the only kinds of gun legislation the NRA has supported. (Last year the gun-rights group pushed a bill introduced by Republican Sen. John Cornyn of Texas, the stated intention of which was to keep guns out of the hands of the mentally ill, but which gun-violence-prevention groups said would actually make it easier for the mentally ill to obtain guns.)
The Obama administration has tried to address concerns about keeping guns away from mentally disturbed individuals through a series of executive actions introduced at the beginning of this year. President Obama proposed investing $500 million in mental-health care, and ordered the Social Security Administration and the the Department of Health and Human Services to share information about mentally ill beneficiaries with the federal background-check system.
In 2014, Rep. Mike Thompson introduced a bill designed to keep guns out of the hands of mental-health patients and convicted criminals that ultimately stalled in the Republican-controlled House.
3. A terror watch list amendment
In 2013 and 2014, Omar Mateen was placed on the federal government's terror watch list, according to the LA Times.
FBI Director James Comey discussed the circumstances under which Mateen came to the bureau's attention in a press conference Monday. A coworker reported his suspicions about Mateen to the FBI after he bragged about a family connection to Al Qaeda, Comey said. "He also said that he was a member of Hezbollah, which is a Shia terrorist organization that is a bitter enemy of the so-called Islamic state, ISIL. He said he hoped that law enforcement would raid his apartment and assault his wife and child so that he could martyr himself," he said.
Agents in the bureau's Miami office investigated Mateen — "introducing confidential sources to him, recording conversations with him, following him, reviewing transactional records from his communications and searching all government holdings for any possible connections" and, finally, interviewing him, Comey said — before the investigation was ultimately closed. It was reopened when an acquaintance of Mateen's carried out a suicide bombing in Syria in 2014. The case was closed a second time after FBI agents determined Mateen did not know the man well.
In one of the most galling examples of Republican obstruction to what President Obama terms "common-sense" gun restrictions, Senate Republicans in December voted down a measure that would have prevented individuals on the terror watch list from purchasing guns, in a 45-to-54 vote. Senate Majority Whip Cornyn called the provision "un-American," noting that individuals have at times in the past been put on the watch list erroneously.
A Quinnipiac poll found that 77 percent of Americans supported changing current laws to prevent suspects on the terror watch list from purchasing a gun.
4. A reinstated assault-weapons ban
Of the 21 deadliest shootings in U.S. history, only two occurred in the ten-year stretch in which the federal assault-weapons ban was active. Twelve of the nation's deadliest shootings — including the top three most lethal incidents — have taken place since the legislation expired in 2004.
In the wake of Sunday's attack in Orlando, presumptive Democratic nominee Hillary Clinton called for a reinstatement of the federal assault-weapons ban that prohibited the sale of guns similar to the AR-15-style semi-automatic rifle Mateen used, up until the ban expired in 2004.
"In Orlando and San Bernardino, terrorists used assault weapons, the AR-15, and they used it to kill Americans. That was the same assault weapon used to kill those little children in Sandy Hook," Clinton said Monday. "We have to make it harder for people who should not have those weapons of war, and that may not stop every shooting or every terrorist attack. But it will stop some, and it will save lives."
This was an uncharacteristically bold move for Clinton; the most recent poll to survey Americans' opinions on the assault-weapons ban, in December 2015, found support for the ban was at a all-time low: just 45 percent of Americans were in favor of it, compared to a high of 80 percent back in 1994. Fifty-three percent opposed it.
5. Laws limiting high-capacity magazines
The Sig Sauer MCX assault rifle Mateen used in Orlando has a magazine that can carry up to 30 bullets: a high-capacity magazine. High-capacity magazines allow a gunman to fire dozens of rounds without stopping to reload — allowing them to inflict maximal damage in minimal time.
According to the Law Center to Prevent Gun Violence, large-capacity magazines, which the center found are used in 50 percent of mass shootings, result in 135 percent more people shot in an incident and increase deaths by 57 percent.
A majority of Americans — 62 percent according to a 2012 Gallup poll — supporting banning high-capacity magazines. For the last three years, legislators around the country have undertaken efforts to ban high-capacity magazines.
The states of California, Colorado, Connecticut, Maryland, Massachusetts, New Jersey and New York as well as the District of Columbia all ban the use of high-capacity magazines in any type of gun.
In February of last year, Sen. Bob Menendez introduced the Large Capacity Ammunition Feeding Device Act, that would ban large capacity magazines at the federal level. It remains mired in Senate Judiciary committee. Rep. Elizabeth Esty of Connecticut introduced the same bill in the House; it likewise remains stuck in the House judiciary committee. GovTrack estimates the laws a 1 percent and 2 percent chance of passing, respectively.
Watch four pro-gun arguments we're sick of hearing.