Early Sunday morning, American Omar Mateen opened fire in an Orlando nightclub, killing 49 people and 53 others hospitalized in what is now the worst mass shooting in U.S. history.
Here's what we know about the mass shooting in Orlando so far:
1. 49 dead in worst mass shooting in United States history
While mass shootings have become all-too common in the U.S. – there have been more than 200 mass killings in the last decade – the massacre in Orlando is the deadliest in US history. In addition to the 49 dead, 53 people have been hospitalized. The previous record for number of deaths was 32, in the 2007 shooting at Virginia Tech. The casualties were originally reported to be 50, but authorities later corrected it to 49; the 50th fatality was the gunman.
2. The shooter
Omar Mateen, 29, was born in New York in 1986 to Afghani parents. Having been an employee of the global security company, G4S, Mateen was a licensed security officer with a firearm license since September 2011.
In 2013, the FBI was suspicious over "inflammatory comments" Mateen had made to co-workers about having ties to terrorism. The investigation was shortly closed afterward, as there was no substantial evidence to support the claims.
In 2014, Mateen also came under investigation by the FBI for vague connections to U.S. citizen Moner Mohammad Abu-Salha, who blew himself up in a suicide attack in Syria.
Mateen's father Seddique Mir Mateen emphasized that Mateen's crime had not been motivated by religion, according to NBC News . The mass shooting comes months after Mateen saw two men kissing in downtown Miami. His father claimed that the scene had angered Omar but that he did not expect his son to commit such a horrendous crime.
Mateen's ex-wife described him as unstable, using the words "mentally ill" and "disturbed", according to the Washington Post . Although no evidence has emerged linking Mateen to terrorist groups, law enforcement told NBC News that he swore allegiance to Abu Bakr al-Baghdadi, the leader of ISIS, in a phone call to 911 prior to the shooting at Pulse.
3. The victims
The city of Orlando has issued a statement ensuring everyone that they are doing all that they can to get as much information out to the families and loved ones of those affected as soon as possible. Many of those who died in the shooting have not yet been identified. According to the city's statement, there have been 18 victims whose next of kin have been notified and the victim's death confirmed.
The victims are of all ages, ranging from 20 years old to 50 years old, some of whom were university students.
Juan Ramon Guerrero, 22, was a student at the University of Central Florida.
Many of those hospitalized are in critical condition, according to the Orlando Regional Medical Center, calling on people to donate blood to help those in need via OneBlood .
4. The gun used
Omar Mateen used an AR-15 style rifle, a gun which some are calling "the gold standard for mass murder" according to the Washington Post .
Since July 2015, seven of the eight high-profile mass shootings that took place have involved the use of an assault-style rifle.
The AR-15 was first designed in 1957 for the U.S. Army, which requested a high velocity rifle that would be "able to penetrate both sides of a standard Army helmet at 500 meters," according to ar15 .
The assault style weapons were outlawed in 1994. However, the ban expired in 2004 and has not been renewed since. The AR-15 is much easier to buy in Florida than a pistol.
In Florida, potential gun owners do not need a license to own or buy a rifle, shotgun or handgun. All one has to do is fill out an ID form and pay an $8 fee for a background check that checks for convicted felons, domestic abusers and a check to see if the purchaser has ever been declared a danger.
5. The place
The shooting took place at Pulse, a gay nightclub otherwise known as "Orlando's Latin Hotspot." The shooting took place during its weekly "Upscale Latin Saturdays" party at around 2 a.m.
The club had posted a warning on its Facebook page telling everybody to get out. "Everyone get out of pulse and keep running," Pulse wrote.
The shooting comes a week after Orlando celebrated gay pride week.
Co-founded by Barbara Poma, the club was established in 2004 in honor of her brother, John, who died of AIDS-related illness in 1991.
6. ISIS connection
ISIS has claimed responsibility for the shooting in a message attributed to an unnamed source which had been passed along over the Telegram messaging app Sunday afternoon.
The terrorist group said the attack was "carried out by an Islamic fighter," according to the NY Times .
This comes after FBI officials confirmed the shooter pledged allegiance to ISIS in a 911 call moments before the shooting took place.
However, as TIME explained, these "claims underline a pattern in which ISIS seeks to inspire sympathizers to carry out attacks — with or without operational support from the group — and then claims responsibility for the carnage after the fact. In such plots, the connection to ISIS as a central organization may exist only in the attacker’s mind, but the resulting violence is no less lethal."
The mass shooting comes weeks after a top ISIS official released an audio recording calling for attacks throughout the world during the holy month of Ramadan, according to the NY Times .
ISIS spokesman Abu Muhammad al-Adnani called for “a month of calamity everywhere for the non-believers."